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NATURAL SCIENCE 



BOOKS BY ARABELLA B. BUCKLEY. 



The Fairy-Land of Science. 

With 74 Illustrations. 12mo. Cloth, gilt, 

$1.50. 

Through Magic Glasses, 

and other Lectures. A Sequel to " The Fairy- 
Land of Science." Illustrated. 12mo. Cloth, 
gilt, $1.50. 

Life and Her Children: 

Glimpses of Animal Life from the Amoeba to 
the Insects. With over' 100 Illustrations. 
12mo. Cloth, gilt, $1.50. 

Winners in Life's Race; 

or, The Great Backboned Family. With 
numerous Illustrations. 12mo. Cloth, gilt, 
$1.50. 

A Short History of Natural Science, 

and of the Progress of Discovery from the Time 
of the Greeks to the Present Time. New edi- 
tion, revised and rearranged. With 77 Illus- 
trations. 12mo. Cloth, $2.00. 

Moral Teachings of Science. 

12mo. Cloth, 75 cents. 



D. APPL.ETON & CO., Publishers, New York. 



s 

D 

ft- 






SUN 
SPECTRUM 



HYDROGEN STAR 

ALOEBARAN 



A SHORT HISTORY OF 

NATURAL SCIENCE 



AND OF THE PROGRESS OF DISCOVERY 

FROM THE TIME OF THE GREEKS TO THE 

PRESENT DAY 



FOR THE USE OF SCHOOLS AND YOUNG PERSONS 



BY 

ARABELLA B. BUCKLEY 

(Mrs. FISHER) 

AUTHOR OF ' THE FAIRY LAND OF SCIENCE ; ' ' LIFE AND HER CHILDREN ; 
'WINNERS IN LIFE'S RACE,' ETC. 



NEW EDITION, REVISED AND RE-ARRANGED 



NEW YORK 
D. APPLETON AND COMPANY 

1893 



QiZ.5 



Authorized Edition. 



<3ift from 
Mrs. Etta F. Winter 
Sept. 20 1932 






DEDICATION TO THE FIRST EDITION 

Zq t£e ifljlemor^ of 

MY BELOVED AND REVERED FRIENDS. 

Sir CHARLES and Ladv LYELL 

TO WHOM I OWE MORE THAN I CAN EVER EXPRESS 

31 Deuicate tfyis mp jfirst 3Soo& 

TRUSTING THAT IT MAY HELP 

TO DEVELOP IN THOSE WHO READ IT THAT 

EARNEST AND TRUTH-SEEKING SPIRIT IN THE STUDY OF 

GOD'S WORKS AND LAWS WHICH WAS THE 

GUIDING PRINCIPLE OF 

THEIR LIVES 



PREFACE TO FIRST EDITION. 



It is not without some anxiety that I offer this little work 
to the public, for it is, I believe, the first attempt which has 
been made to treat the difficult subject of the History of 
Science in a short and simple way. 1 

Its object is to place before young and unscientific 
people those main discoveries of science which ought to be 
known by every educated person, and at the same time to 
impart a living interest to the whole, by associating with each 
step in advance some history of the men who made it. 

During the many years that I enjoyed the privilege of 
acting as secretary to the late Sir Charles Lyell, and was 
thus brought in contact with many of the leading scientific 
men of our day, I often felt very forcibly how many 
important facts and generalisations of science, which are of 
great value both in the formation of character and in giving 
a true estimate of life and its conditions, are totally un- 
known to the majority of otherwise well-educated persons. 

Great efforts are now being made to meet this difficulty, 

1 Mr. Baden Powell's excellent little ' History of Natural Philo- 
sophy,' published in Lardner's 'Cyclopaedia' in 1834, is scarcely 
intended for beginners, and does not extend farther than the seventeenth 
century. This is the only work of the kind I have been able to find. 



PREFACE TO FIRST EDITION. 



by teaching children a few elementary facts of the various 
branches of science; but, though such instruction is of 
immense value, something more is required in order that 
the mind may be prepared to follow intelligently the great 
movement of modern thought. The leading principles of 
science ought in some measure to be understood ; and these 
will, I believe, be most easily and effectually taught by 
showing the steps by which each science has attained its 
present importance. 

It is this task which I have endeavoured to accomplish ; 
and if teachers will make their pupils master the explana- 
tions given in these pages and, wherever it is possible, try 
the experiments suggested, I venture to hope that this little 
work may supply that modest amount of scientific informa- 
tion which every one ought to possess, while, at the same 
time, it will form a useful groundwork for those who wish 
afterwards to study any special branch of science. 

The plan adopted has been to speak of discoveries in 
their historical order, and to endeavour to give such a 
description of each as can be understood by any person of 
ordinary intelligence. This has made it necessary to select 
among subjects of equal importance those which could be 
dealt with in plain language, and to avoid passing allusions 
to such as did not admit of such explanation. 

The history of the nineteenth century has been a very 
difficult and I fear scarcely a successful task; for, while 
those who know anything of the subjects mentioned will 
feel that the account is very defective owing to so much 
being left out, the beginner will probably find it difficult 



PREFACE TO FIRST EDITION. 



owing to so much being put in. The reproach on both 
sides would be just, yet it seemed better to give even a few 
of the leading discoveries and theories of our own time than 
to leave the student with such crude ideas of many branches 
of science as he must have had if the history had ended 
with the eighteenth century. 

When treating of such varied subjects, many of them pre- 
senting great difficulties both as regards historical and scien- 
tific accuracy, I cannot expect to have succeeded equally 
in all, and must trust to the hope of a future edition to 
correct such grave errors as will doubtless be pointed out, 
in spite of the care with which I have endeavoured to verify 
the statements made. 

As the size of the book makes it impossible to give the 
numerous references which would occur on every page, I 
have named at the end of each chapter a few of the works 
consulted in its preparation, choosing always in preference 
those which will be useful to the reader if he cares to refer 
to them. I had also prepared questions on the work; but 
those competent to give an opinion, tell me that teachers 
in these days prefer to prepare their own lessons. I have 
therefore substituted, at p. 481, a chronological table of the 
various sciences, by means of which questions can be 
framed, either upon the discoveries of any given period, or 
on the progressive advance, through several centuries, of 
any of the five main divisions of science which are dealt 
with in this volume. 

In conclusion, I wish to acknowledge my obligations to 
many kind friends, and especially to Mr. A. R. Wallace 



PREFACE TO FIRST EDITION. 



and Mr. J. C. Moore, F.R.S., who have rendered me very 
material and valuable assistance. I am also much indebted 
to the Rev. R. M. Luckock, of the Godolphin Grammar 
School, who read the whole work in manuscript, with a view 
to pointing out any portions which might be unintelligible 
to schoolboys. 



London, December 1875. 



PREFACE 
TO THE FOURTH EDITION 



Thirteen years have now elapsed since this work was first 
published, and in the two intervening editions every care 
was taken to revise the text and to add information as 
to new discoveries. The subjects of Molecular Physics, 
Electro-magnetism, and Botany were all more fully treated, 
and a chapter was added to the science of the eighteenth 
century dealing with the experiments of Sauveur and 
Chladin on musical vibrations. 

In the present edition, besides careful revision, a further 
and somewhat important change has been made. The 
recent advances in science had all hitherto been treated 
together in a final chapter, and were in consequence often 
overlooked. The latter part of the volume has now been 
recast, and each branch of science brought up separately 
to our present knowledge so far as space will allow. 
Scanty as references to modern discoveries must necessarily 
be in a small work of this kind, they nevertheless awaken 
a desire to know more, and I venture to hope that for 
young students the book is now a fair introduction to the 
study of science. 

Upcott Avenel, 

October 1888. 



CONTENTS. 



Introduction. ••...<•• 
PART I. 

SCIENCE OF THE GREEKS. 

CHAPTER I. 

639 TO 470 B.C. 

Ignorance of the Greeks concerning Nature — Ionian School of 
Learning — Thales discovers the Solstices and Equinoxes, and 
knows that the Moon Reflects the Light of the Sun — Anaxi- 
mander invents a Sun-dial — Discovers the Phases of the Moon 
— Makes a Map of the Ancient World — Pythagoras teaches 
that the Earth moves, and that the Morning and Evening Star 
are the same — He studies Geology, and knows that Land has 
in some places become Sea — True sayings of Pythagoras and 
his Followers about Geology — Invention of the Monochord . 

CHAPTER II. 

499 to 322 B.C. 

Anaxagoras studies the Moon — Describes Eclipses of the Sun and 
Moon — Is Tried and Condemned for Denying that the Sun is 
a God — Hippocrates the Father of Medicine — Separates the 
office of Priest and Doctor — Studies the Human Body — 
Eudoxus has an Observatory — Makes a Map of the Stars — 
Explains the Movements of the Planets — Democritus studies 
the Milky Way — Aristotle an Astronomer and Zoologist — 
Divides Animals into Classes — Teaches that there is a Gradual 
Succession of Animal Life — Studies the Difference of the Life 
in Plants und Animals — Theophrastus the first Botanist 



1AGE 

1 



CONTENTS. 



CHAPTER III. 
320 TO 212 B.C. 

PAGE 

School of Science at Alexandria— The Ecliptic and the Zodiac — 
Greeks believed that the Sun moved round the Earth — Aris- 
tarchus knew that it was the Earth which moved — He also 
knew of the Obliquity of the Ecliptic, and that the Seasons 
are caused by it — He knew that the Earth turns daily on its 
Axis — Euclid discovers that Light travels in straight lines — 
Archimedes discovers the Lever — Principle of the Lever — 
Hiero's Crown, and how Archimedes discovered the principle 
of Specific Gravity — Screw of Archimedes . • . .18 



CHAPTER IV. 

280 TO I20 B.C. 

Erasistratus and Herophilus study the Human Body — Eratosthenes 
the Geographer lays down the First Parallel of Latitude and 
the First Meridian of Longitude — He measures the circumfer- 
ence of the Earth — Hipparchus writes on Astronomy — Cata- 
logues 1080 Stars — Calculates when Eclipses will take place 
— Discovers the Precession of the Equinoxes . . . 



CHAPTER V. 

FROM A.D. 70 TO 200. 

Ptolemy founds the Ptolemaic System — He writes on Geography 
— Strabo, a great traveller, writes on Geography — Studies 
Earthquakes and Volcanoes — Pliny the Naturalist — Galen the 
greatest Physician of Antiquity — Describes the two Sets of 
Nerves — Proves that Arteries contain Blood — Lays down a 
theory of Medicine — Greece and her Colonies conquered by 
Rome — Decay of Science in Greece — Concluding remarks on 
Greek Science 32 



CONTENTS. 



PART II. 

SCIENCE OF THE MIDDLE AGES. 

CHAPTER VI. 

SCIENCE OF THE ARABS. 

PAGE 

Dark Ages of Europe — The Arabs, checked in their conquests by 
Charles Martel, settle down to Science — The Nestorians and 
Jews translate Greek Works on Science — Universities of the 
Arabs — Chemistry first studied by the Arabs — Alchemy, or the 
attempt to make Gold — Hermes the first Alchemist — Hermeti- 
cally-sealed Tubes — Gases and Vapours called ' Spirits' by the 
Arabs . 39 

CHAPTER VII. 

SCIENCE OF THE ARABS (CONTINUED). 

Geber, or Djafer, the founder of Chemistry — His Explanation of 
Distillation — Of Sublimation — Discovers that some Metals in- 
crease in weight when heated — Discovers strong Acids — Nitric 
Acid — Sulphuric Acid — Discovery of Sal-Ammoniac by the 
Arabs — Arabs mix up Astronomy with Astrology — Albateg- 
nius calculates the Length of the Year — Mohammed Ben 
Musa, first writer on Algebra — Uses the Indian Numerals — 
Gerbert introduces them into Europe — Alhazen's discoveries in 
Optics — His Explanation why only one image of each object 
reaches the Brain — His discovery of Refraction, and of its 
effect on the light of the Sun, Moon, and Stars — His discovery 
of the magnifying power of rounded glasses . . . . 43 

CHAPTER VIII. 

SCIENCE OF THE MIDDLE AGES IN EUROPE. 

Roger Bacon — His c Opus Majus' — His Explanation of the Rain- 
bow — He makes Gunpowder — Studies Gases — Proves a Candle 
will not burn without Air — His Description of a Telescope — 



xvi CONTENTS. 



PAGB 

Speaks of Ships going without Sails — Flavio Gioja invents the 
Mariner's Compass — Greeks knew of the Power of the Load- 
stone to attract Iron — Use of the Compass in discovering new 
lands — Invention of Printing — Columbus discovers America — 
Vasco de Gama sees the Stars of the Southern Hemisphere — 
Magellan's ship sails round the World — Inventions of Leonardo 
da Vinci . . . . . . . • • • 5* 



PART III. 
RISE AND PROGRESS OF MODERN SCIENCE. 

CHAPTER IX. 

SCIENCE OF THE SIXTEENTH CENTURY. 

Rise of Modern Science — Dogmatism of the Middle Ages — 
Reasons for studying discoveries in the order of their dates — 
Copernican theory of the Universe — Copernicus goes back to 
the System of Aristarchus — Is afraid to publish his Work till 
quite the end of his Life — Work of Vesalius on Anatomy — He 
shows that Galen made many mistakes in describing Man's 
Structure — His Banishment and Death — The value of his 
Work to Science — Fallopius and Eustachius Anatomists — 
Gesner's Works on Animals and Plants — He forms a Zoolo- 
gical Cabinet and makes a Botanical Garden — His Natural 
History of Animals — His classification of Plants according to 
their Seeds — His work on Mineralogy — Csesalpinus makes the 
First System of Plants on Gesner's plan — Explains Dioecious 
Plants — Chemistry of Paracelsus and Van Helmont . .61 

CHAPTER X. 

SCIENCE OF THE SIXTEENTH CENTURY (CONTINUED) 

Baptiste Porta discovers the Camera Obscura — Shows that our 
Eye is like a Camera Obscura — Makes a kind of Magic Lan- 
tern by Sunlight — Kircher afterwards makes a Magic Lantern 
by Lamplight — Dr. Gilbert's discoveries in Electricity — Tycho 



CONTENTS. 



PAGE 

Brahe, the Danish Astronomer — Builds an Observatory on the 
Island of Huen — Makes a great number of Observations, and 
draws up the Rudolphine Tables — Galileo discovers the prin- 
ciple of the Pendulum — Calculates the velocity of Falling 
Bodies, and shows why it increases — Shows that Unequal 
Weights fall to the Ground in the same time — Establishes the 
relations of Force and Weight — Studies musical Sounds — 
Stevinus on Statics — Summary of the Science of the sixteenth 
century .......... 72 



CHAPTER XI. 

SCIENCE OF THE SEVENTEENTH CENTURY. 

Astronomical discoveries of Galileo — The Telescope — Galileo ex- 
amines the Moon, and discovers the Earth-light upon it — Dis- 
covers Jupiter's four Moons — Distinguishes the Fixed Stars from 
the Planets — The phases of Venus confirm the Copernican 
theory — Galileo notices Saturn's Ring, but does not distin- 
guish it clearly — Observes the spots on the Sun — The Inquisi- 
tion force him to deny the movement of the Earth — Blindness 
and Death of Galileo 



CHAPTER XII. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Kepler the German Astronomer — Succeeds Tycho as Mathema- 
tician to the Emperor Rudolph — His description of the Eye — 
He tries to explain the orbit of the planet Mars — And by com- 
paring Tycho's tables with observation discovers his First and 
Second Law. of the movements of the Planets — His delight at 
Galileo's discoveries — Kepler's Third Law — Comparison of the 
labours of Tycho, Galileo, and Kepler . . . 93 



CONTENTS. 



CHAPTER XIII. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

PAGE 

Francis Bacon, 1561-1626 — He teaches the true method of 
studying Science in his ' Novum Organum ' — Rene Descartes, 
1 596- 1 650 — He teaches that Doubt is more honest than Ignor- 
ant Assertion — Willebrord Snellius discovers the Law of Re- 
fraction, 1621 — Explanation of this Law • • IOI 

CHAPTER XIV. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Fabricius Aquapendente discovers Valves in the Veins — Harvey's 
discovery of the Circulation of the Blood — Discovery of the 
Vessels which carry nourishment to the Blood — Gaspard 
Asellius notices the Lacteals — Pecquet discovers the Passage 
of the fluid to the Heart — Riidbeck discovers the Lymphatics 108 

CHAPTER XV. 
SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Torricelli discovers the reason of Water rising in a Pump — Uses 
Mercury to measure the Weight of the Atmosphere — Makes 
the First Barometer — M. Perrier, at Pascal's suggestion, de- 
monstrates variations in the pressure of the atmosphere — Otto 
Guericke invents the Air-pump — Working of the Air-pump — 
Guericke proves the Pressure of the Atmosphere by the experi- 
ment of the Magdeburg Spheres — He makes the first Electrical 
Machine — Foundation of Royal Society of London and other 
Academies of Science . . . . . .114 

CHAPTER XVI. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Boyle's Law of the Compressibility of Gases — This same Law dis- 
covered independently by Marriotte — Hooke's theory of Air 



CONTENTS. 



PAGB 

being the cause of Fire — Boyle's experiments with Animals 
under the Air-pump — John Mayow, the greatest Chemist of the 
Seventeenth Century — His experiments upon the Air used in 
Combustion — Proves that the same portion is used in Respira- 
tion — Proves that Air which has lost its Fire-air is Lighter — 
Mayow's ' Fire-air ' was Oxygen, and his Lighter Air Nitrogen 
— He traces out the effect which Fire-air produces in Animals 
when Breathing . . . . . • . .126 



CHAPTER XVII. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Malpighi first uses the Microscope to examine Living Structures 
— He describes the Air-cells of the Lungs — Watches the Cir- 
culation of the Blood — Observes the Malpighian Layer in the 
Human Skin — Describes the Structure of the Silkworm — 
Leeuwenhoeck discovers Animalcules — Grew and Malpighi 
discover the Cellular Structure of Plants — The Stomates in 
Leaves — They study the Germination of Seeds — Ray and 
Willughby classify and describe Animals and Plants — The 
Friendship of these two Men . . . • . .134 

CHAPTER XVIII. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

1642, Birth of Newton — His Education — 1666, His three great 
Discoveries first occur to him — Method of Fluxions and Dif- 
ferential Calculus — First thought of the Theory of Gravitation 
— Failure of his Results in Consequence of the Faulty Measure- 
ment of the size of the Earth — 1682, Hears of Picart's new 
Measurement — Works out the result correctly, and proves the 
Theory of Gravitation — Explanation of this Theory — Estab- 
lishes the Law that Attraction varies inversely as the squai-es 
of the distance — Explains the transmission of sound — 1687, 
Publishes the 'Principia' — Some of the Problems dealt with 
in this Work . 144 



CONTENTS. 



CHAPTER XIX. 
SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

PAGB 

Transits of Mercury and Venus — Kepler foretells their occurrence 
— 163 1, Gassendi observes a transit of Mercury — 1639, Hor- 
rocks foretells and observes a Transit of Venus — 1676, Halley 
sees a Transit of Mercury, and it suggests to him a method for 
Measuring the Distance of the Sun — 1691-1716, Halley de- 
scribes this method to the Royal Society — Explanation of 
Halley's method 1 53 



CHAPTER XX. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Newton's Discovery of the Dispersion of Light — Traces the 
amount of Refraction of each of the Coloured Rays — Makes a 
Rotating Disc turning the colours of the Spectrum into White 
Light — Reason why all Light passing through glass is not 
Coloured — Mr. Chester More Hall discovers the Difference of 
Dispersive Power in Flint and Crown Glass — Newton's Papers 
destroyed by his pet dog — Last years of Newton's life . . 161 

CHAPTER XXI. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Roemer measures ■ the Velocity of Light — Newton's Corpuscular 
Theory of Light — Undulatory or Wave Theory proposed by 
Huyghens — Invention of Cycloidal Pendulums by Huyghens — 
Discovery of Saturn's Ring — Sound caused by Vibration of 
Air — Light by Vibration of Ether — Reasons why we see 
Light — Reflection of Waves of Light — Cause of Colour — Re- 
fraction explained by the Undulatory Theory — Mr. Tylo^s 
Illustration of Refraction — Double Refraction explained by 
Huyghens — Polarization of Light not understood till the 
nineteenth century 172 



CONTENTS. xxi 



CHAPTER XXII. 

PAGB 

Summary of the Science of the Seventeenth Century . 182 



CHAPTER XXIII. 

SCIENCE OF THE EIGHTEENTH CENTURY. 

Great spread of Science in the Eighteenth Century — Advance of 
the Sciences relating to Living Beings — Foundation of Leyden 
University in 1574 — Boerhaave, Professor of Medicine at Ley- 
den, 1 70 1 — Foundation of Chemistry of organic compounds 
by Boerhaave — Influence of Boerhaave upon the study of Medi- 
cine — Belief of the Alchemists in * Vital Fluids ' — Boerhaave's 
Experiments on the Juices of Plants — Dr. Hales's Experiments 
on Plants — Boerhaave's Analyses of Milk, Blood, etc. — Great 
popularity of his Chemical Lectures 189 



CHAPTER XXIV. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

Childhood of Haller — Foundation of the University of Gottingen 
in 1736 — Haller made Professor of Anatomy — Haller's Ana- 
tomical Plates — He discovers the power of Contraction of the 
Muscles — Rise of Comparative Anatomy — John Hunter's in- 
dustry in Dissecting and Comparing the Structures of different 
Animals — His Museum and the arrangement of his Collection 
— Bonnet's Experiments on Plants— Experiments upon Ani- 
mals by Bonnet and Spallanzani — Regrowth of different parts 
when cut off — Bonnet's theory of Gradual Development of 
Plants and Animals — Anatomical Works of Haller — He dis- 
covers the power of the Muscles to contract . . . . 195 



CONTENTS. 



CHAPTER XXV. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

PAGE 

Birth and Early Life of Buffon and Linnaeus compared — Buffon's 
Work on Natural History — Daubenton wrote the Anatomical 
Part — Buffon's Books very interesting, but not always accurate 
— He first worked out the Distribution of Animals — Struggles 
of Linnaeus with Poverty — Mr. Clifford befriends him — He 
becomes Professor at Upsala — He was the first to give Specific 
Names to Animals and Plants — Explanation of his Descriptions 
of Plants — Use of the Linnaean or Artificial System — After- 
wards superseded by the Natural System — Linnaeus first used 
accurate terms in describing Plants and Animals — Character 
of Linnaeus — Sale of his Collection, and Chase by the Swedish 
Man-of-war •••••»«. 203 



CHAPTER XXVI. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

The Study of the Earth neglected during the Dark Ages — Preju- 
dices concerning the Creation of the World — Attempts to Ac- 
count for Buried Fossils — Palissy, the Potter, first asserted 
that Fossil-shells were real Shells — Scillas Work on the Shells 
of Calabria, 1 6 70 — Woodward's Description of Different For- 
mations, 1695 — Lazzaro Moro one of the first to give a true 
explanation of the facts — Abraham Werner lectures on Miner- 
alogy and Geology, 1775 — Disputes between the Neptunists 
and Vulcanists — Dr. Hutton first teaches that it is by the Study 
of the Present that we can understand the Past — Theoiy of 
Hutton — Sir J. Hall's Experiments upon Melted Rocks — 
Hutton discovers Granite Veins in Glen Tilt — William Smith, 
the ' Father of English Geologists ' — His Geological Map of 
England . . . . . . . . . . 2i 



CONTENTS. xxiil 



CHAPTER XXVII. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

PAGH 

Birth of Modern Chemistry — Discovery of ' Fixed Air,' or Car- 
bonic Acid, by Black and Bergmann — Working out of 'Che- 
mical Affinity ' by Bergmann — He tests Mineral Waters, and 
proves ' Fixed Air ' to be an Acid — Discovery of Hydrogen by 
Cavendish — He investigates the Composition of Water — Oxy- 
gen discovered by Priestley and Scheele — Priestley's Experi- 
ments — He fails to see the true bearing of his Discovery — His 
Political Troubles and Death — Nitrogen described by Dr. 
Rutherford — Lavoisier lays the Foundation of Modern Chem- 
istry — He destroys the Theory of ' Phlogiston ' by proving that 
Combustion and Respiration take up a Gas out of the Air — 
Discovers the Composition of Carbonic Acid and the nature 
of the Diamond — French School of Chemistry — Death of 
Lavoisier .......,,. 224 

CHAPTER XXVIII. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

Doctrine of Latent Heat, taught by Dr. Black in 1760 — Water 
containing Ice remains always at o° C, and Boiling Water at 
ioo° C, however much Heat is added — Black showed that 
the lost Heat is absorbed in altering the condition of the Water 
— Watt's Application of the Theory of Latent Heat to the 
Steam-engine — Early History of Steam-engines — Newcomen's 
Engine — Watt invents the Separate Condenser — Diagram of 
Watt's Engine — Difficulties of Watt and Boulton in introduc- 
ing Steam-engines ........ 240 

CHAPTER XXIX. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

Benjamin Franklin born, 1 706 — His Early Life — Du Faye dis- 
covers two kinds of Electricity — Franklin proves that Elec- 
tricity exists in all Bodies, and is only developed by Friction 



CONTENTS. 



PAGB 

— Positive and Negative Electricity — Franklin draws down 
Electricity from the Sky — Invents Lightning-conductors — 
Discoveiy of Animal Electricity by Galvani — Controversy 
between Galvani and Volta — Volta proves that Electricity can 
be produced by the Contact of two Metals — Electrical Batteries 
— The Crown of Cups — The Voltaic Pile . . . 252 



CHAPTER XXX. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

Calculation of musical Vibrations, Sauveur — Experiments on 
Vibrations of Strings — Bernoulli. Euler, Lagrange — Four 
Conditions determining the pitch of a Stretched String — The 
Octave — Nodes and Segments in a Vibrating String — Over- 
tones or Harmonics — Chladni — Discovers Mode of Vibration 
of Metal and Glass Plates — Vibration of Bells and Gongs — 
Sand Figures produced by Vibration 263 



CHAPTER XXXI. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

Bradley and Delisle, Astronomers — Aberration of the Fixed Stars 
— Nutation of the Axis of the Earth, Delisle's Method of 
Measuring the Transit of Venus — Lagrange and Laplace — 
Libration of the Moon accounted for by Lagrange — Laplace 
works out the Long Inequality of Jupiter and Saturn — La- 
grange proves the Stability of the Orbits of the Planets — Sir 
William Herschel constructs his own Telescopes — Discovery 
of a New Planet — Discovery of Binary Stars — Herschel studies 
Star-clusters and Nebulae — Theory of Nebulae being matter out 
of which Stars are made — The Motion of our Solar System 
through Space — Weight of the Earth determined by the 
Schehallion Experiment — Summary of the Science of the 
Eighteenth Century . . . . • . . . 275 



CONTENTS. 



CHAPTER XXXII. 

SCIENCE OF THE NINETEENTH CENTURY. 

PAGE 

Difficulties of Contemporary History — Discovery of Asteroids and 
Minor Planets between Mars and Jupiter — Dr. Olbers suggests 
they may be fragments of a larger Planet— Encke's Comet, and 
the correction of the size of Jupiter and Mercury — Biela's 
Comet, noticed in 1826 — It divides into two Comets in 1845 — 
Irregular movements of Uranus — Adams and Leverrier calcu- 
late the position of an Unknown Planet — Neptune found by 
these calculations in 1846 — A Survey of the whole Heavens 
made by Sir John Herschel — His work in Astronomy — 
Comets and Meteor-systems — Use of improved Telescopes in 
discovery — Leverrier's analysis of Planetary Orbits . . 297 

CHAPTER XXXIII. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Discoveries concerning Light made in the Nineteenth Century — 
Birth and History of Dr. Young — He explains the Interference 
of Light — Cause of Prismatic Colours in a Shadow — And in a 
Soap-bubble — Malus discovers the Polarization of Light caused 
by Reflection — Birth and History of Fresnel — Polarization of 
Light explained by Young and Fresnel — Complex Vibrations 
of a Ray of Light — How these Waves are reduced to two 
separate Planes in passing through Iceland-spar — Sir David 
Brewster and M. Biot explain the colours produced by Polar- 
ization — Fizeau and Foucault on Velocity of Light — Colour 
Theory of Young and Helmholtz . . . . . 315 

CHAPTER XXXIV. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

History of Spectrum Analysis — Discovery of Heat-rays by Sir W. 
Herschel — And of Chemical Rays by Ritter of Jena — Photo- 
graphy first suggested by Davy and Wedgwood — Carried out 
by Daguerre and Talbot — Dark Lines in the Spectrum first 

2 



CONTENTS. 



PAGB 

observed by Wollaston — Mapped by Fraunhofer — Life of 
Fraunhofer — He discovers that the Dark Lines are different 
in Sun-light and Star-light — Experiments on the Spectra of 
different Flames — Four new Metals discovered by Spectrum 
Analysis — Artificial Dark Lines produced in the Spectrum by 
Sir David Brewster — Bunsen and Kirchhoff explain the Dark 
Lines in the Solar Spectrum — Metals in the Atmosphere of 
the Sun — Photosphere — Corona — Jannsen and Lockyer on 
Red Prominences — Chromosphere — Huggins and Miller ex- 
amine the Stars and Nebulae by Spectrum Analysis — Spectra 
of Comets — Travelling Stars — Celestial Photography . . 330 

CHAPTER XXXV. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Early Theories about Heat — Count Rumford shows that Heat 
can be produced by Friction — He makes Water boil by boring 
a Cannon — Davy makes two pieces of Ice melt by Friction — 
His conclusion about Heat — How ' Latent Heat ' is explained 
on the theory that Heat is a kind of Motion — Dr. Mayer sug- 
gests the Determination of the Mechanical Equivalent of Heat 
— Dr. Joule's Experiments on the Mechanical Equivalent of 
Heat — Dr. Hirn's Experiments on the conversion of Heat into 
Motion — Proof of the Indestructibility and Conservation of 
Energy — Theory of dissipation of Energy — Molecular Theory 
of Gases — Free Molecules in Vacuum Tubes . . . 349 

CHAPTER XXXVI. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Oersted discovers the effect of Electricity upon a Magnet — 
Electro- Magnetism — Experiments by Ampere on Magnetism 
and Electricity — Ampere's Early Life — Direction of the 
North Pole of the Magnet depends on the course of the 
Electric Currents — Lines of Magnetic Force between two 
Electric Wires — Electro-Magnets made by means of an 
Electric Current — Arago magnetises a Steel Bar with an 
ordinary Electrical Machine — Faraday discovers the Rotatory 
Movement of Magnets and Electrified Wires — Produces an 



CONTENTS. 



°AGS 

Electric Current by means of a Magnet — Seebeck discovers 
Thermo-Electricity, or the production of Electricity by Heat 
— Schwabe discovers Periodicity of the Spots on the Sun — 
Sabine suggests a connection between Sun-spots and Magnetic 
phenomena — This proved in 1859 by Observations of Carring- 
ton and Hodgson — Electric Telegraph — Wheatstone — Cooke 
— Steinheil — Morse — Bain — Cowper's Telegraph — The Tele- 
phone 367 

CHAPTER XXXVII. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Davy discovers that Nitrous Oxide produces Insensibility — Laugh- 
ing-gas — Safety-lamp, 18 15 — Nicholson and Carlisle discover 
Decomposition of Water, 1 800 — Davy discovers the effect of 
Electricity upon Chemical Affinity — Faraday's Discoveries in 
Electrolysis — Indestructibility of Force — Various Modes dis- 
covered of Decomposing Substances — John Dalton, chemist — 
Law of Definite Proportions — Law of Multiple Proportions — 
Dalton's Atomic Theory — Meta-elements — Liquefaction of per- 
manent Gases — The Study of Organic Chemistry — Liebig, the 
great teacher in Organic Chemistry — Discovery of Aniline Dyes 390 

CHAPTER XXXVIII. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

The Organic Sciences are too difficult to follow out in detail — 
Jussieu's Natural System of Plants — Sprengel on fertilisation 
of Plants by insects — Robert Brown on embryological botany 
— Sir W. Hooker — Goethe proves the Metamorphosis of 
Plants 411 

CHAPTER XXXIX. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Humboldt studies the Lines of Average Temperature on the Globe 
— Extends our knowledge of Physical Geography — Writes the 



CONTENTS. 



PAGH 

'Cosmos' — Death of Humboldt — The three Naturalists, 
Lamarck, Cuvier, and Geoffroy St.-Hilaire — Cuvier begins the 
Museum of Comparative Anatomy — Lamarck's History of 
Invertebrate Animals — G. St.-Hilaire brings Natural History 
Collections from Egypt — Lamarck on the Development of 
Animals — G. St.-Hilaire on 'Homology,' or the similarity in 
the parts of different animals — Cuvier's ' Regne Animal ' and 
his Classification of Animals — Cuvier on the Perfect Agree- 
ment between the Different Parts of an animal — He Studies 
and Restores the Remains of Fossil Animals — His ' Ossemens 
Fossiles ' — Death of Cuvier — Von Baer on the Study of Em- 
bryology — Parker and Balfour on Embryology . , . 423 



CHAPTER XL. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Prejudices which retarded the study of Geology — Sir Charles 
Lyell traces out the Changes going on now — Mud carried 
down by the Ganges — Eating away of Sea-coasts — Eruption of 
Skaptar Jokul — Earthquake of Calabria — Rise and Fall of 
Land — ' Principles of Geology ' published in 1830 — Murchison 
on stratigraphical geology — Louis Agassiz — De Saussure's 
Study of Glaciers — Agassiz on Europe and North America 
being once covered with Ice — Boucher de Perthes on Ancient 
Flint Implements — M'Enery on Flint Implements in Kent's 
Cavern, with Bones of Extinct Animals — Swiss Lake-dwellings 
— ' Antiquity of Man ' — Study of Petrology . . . -441 



CHAPTER XLI. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Facts which led Naturalists to believe that the different kinds of 
Animals are descended from Common Ancestors — All Animals 
of each class formed on one Plan — Embryological Structure — 
Living and Fossil Animals of a country resemble each other — 
Gradual Succession of Animals on the Globe— -Links between 



CONTENTS. 



PAGE 

different species — Darwin's Theory of Natural Selection — 
Wallace worked out the same Theory independently — Sketch 
of the Theory of Natural Selection — Selection of Animals by 
Man — Selection by Natural Causes — Difficulties in Natural 
History which are explained by this Theory — The present 
state of Biological Science — Geographical distribution — Carni- 
vorous Plants — Fertilisation of Plants — Weissman on Germ- 
plasma — Foundation of new Zoological Classifications — Dis- 
coveries of Fossil Animals by Professor Marsh — Links thus 
afforded in the Animal Series — Concluding Remarks on the 
History of Science ........ 457 



A SHORT HISTORY 



NATURAL SCIENCE, 



INTRODUCTION. 

As this little work is to be a history of Natural Science, 
it will be as well to begin by trying to understand what 
Science is. 

The word itself comes from sc/o, I know, and means 
simply knowledge. The science of botany is therefore the 
knowledge of plants ; and the science of astro womy, the know- 
ledge of the heavenly bodies. 

But now comes the question, What kind of knowledge 
is required ? You might be able to tell the names of all 
the plants in the world, and of all the stars in the sky, and 
yet have scarcely any real knowledge of botany or astronomy. 
You will easily understand this if we compare it with some- 
thing you meet with in daily life. Suppose I took you into 
a large school and told you the names of all the children 
there ; even if you learnt these names by heart, you could 
not say you knew the children, or anything about them, 
beyond their names. One might be ill-tempered, another 
good-tempered ; one might have a home and a father and 
mother, another might be an orphan and homeless, and 



HISTORY OF SCIENCE. 



you would find their mere names of no use to you if you 
wished to choose one of them to do any work, or to be 
your friend and companion. For this you would want to 
learn their character, their habits, and other real facts about 
them. 

Now this last is just the kind of knowledge which is 
required in science. If, besides the name of a plant, you 
know its different parts, the shape of its leaves, the number 
of its seeds, and how they are arranged in the seed-vessel, 
the number of stamens or thread-like bodies in the middle 
of the flower, the number and colour of its petals or flower- 
leaves, and many other points like these, then you know 
something of structural botany. If you know, besides, how 
a plant takes up food, how it breathes, and how the sun- 
light acts upon the leaves and alters the juices of the plant, 
then you know something of the life of the plant, or 
physiological bota?iy. If you know where the plant grows 
best, in what soil, in what climate, and in what countries, 
then you know something of geographical botany ; and if 
your knowledge is accurate and carefully learnt it is real 
science. 

By this you will see that science means not merely 
knowledge, but an accurate and clear knowledge about the 
things which we see around us in the universe. In the 
present day, people are beginning to teach children much 
more on these subjects than they did forty years ago, and 
every intelligent boy or girl probably knows that Astronomy 
is the science of the sun, stars, and planets ; Physics and 
Mechanics, the sciences which teach the properties of bodies 
and their laws of motion ; Biology the science of life ; 
Geology the science of the earth, teaching us how the dif- 
ferent rocks have been formed ; and Chemistry the science 
which treats of the materials of which all substances are 



INTRODUCTION. 



made, and shows the changes which take place when two 
substances act upon one another so as to make a new sub- 
stance. 

There are many simple books written now to explain 
these sciences, and those who wish can read these books 
and study the examples and experiments given in them. 
They tell us what science now is, and the explanations 
given by the best men about the universe in which we live. 
But they do not tell us how science has become what it is, 
and it is this which I hope to tell you in the present book. 

A man who wishes to understand a steam-engine can 
do so by going to an engineer and having each part ex- 
plained to him ; but if he wishes to know the history of the 
steam-engine he must go back to the first one ever made, 
and study each new improvement as it arose. And so if 
we go back to the first attempts made by thoughtful men 
to understand nature, and then trace up step by step the 
knowledge gained from century to century, we shall have at 
least a more intelligent understanding of that which is 
taught us now. But if we have any true love of knowledge 
we shall gain far more than this ; for in studying the his- 
tory of those grand and patient men who often spent their 
lives and made great sacrifices to understand the works of 
God, the merest child must feel how noble it is to long and 
strive after truth. 

When we go back to very early ages we do not find 
that people understood much of what we now call science. 
So long as men were chiefly occupied in protecting them- 
selves against other savage men and wild beasts, and had 
to struggle very hard to get food and clothing, they had 
very little time or wish to study nature. Still they learnt 
many things which were necessary for their life. They 



HISTORY OF SCIENCE. 



learnt, for instance, at what times the sun rose and set, for 
upon this their day's work depended. They learnt how 
often the moon was full, so that they could see their way 
by moonlight; and they remaiked very early the times 
when spring, summer, autumn, and winter came round, 
because the sowing of their seeds and the gathering of their 
fruits depended upon these seasons. 

In this way we find that as far back as history goes men 
have always had some knowledge of the facts of nature ; 
and those nations, like the Egyptians and Chinese, which 
long ago had become highly civilised, had learnt a very 
great deal, and must probably have known some things of 
which we are still ignorant. 

There has been a great deal written about the science 
of the Chinese, Indians, and Egyptians, but I shall not tell 
you anything about them here, because their knowledge has 
had very little to do with the science which has come down 
to us, and it would besides be difficult to give you any real 
idea of what they knew without writing a book on the 
subject. 

We will start, therefore, with the Greeks, at the time 
when they first began to try and explain some of the 
natural events which they saw taking place every day. 
This was about the year 700 B.C., when Thales, one of the 
seven wise men, was living, and you will see in the next 
chapter that even at this time, when Greece was famous for 
its learning, the people had still some very strange ideas 
about the working of the universe. 



PAKT I. 
SCIENCE OF THE GREEKS 

FROM B.C. 639 TO A.D. 20(1. 



Chief Men of Science among the Greeks. 









B.C. 




Thales . . . Born about 640. 




Anaximander 


. 610. 




Pythagoras 






. 5OO. 




Anaxagoras . 






499. 




Democritus . 






• 459- 




Hippocrates . , 






- 420. 




Eudoxus 






, 406. 




Aristotle 






• 384- 




Theophrastus 






- 371. 




Aristarchus . 






320. 




Euclid . 






. 30O. 




Archimedes . 






287. 




Erasistratus . 






? 




Ilerophiius . 






? 




Eratosthenes 






276. 




Ilipparchus . 
btrabo . . , 
rtoiemjT 






l60. 
1X0 

50 to A.D. 


18 

IOO. 


Galen , 






■ c 


131. 



ch. i. SCIENCE OF THE GREEKS. 



CHAPTER I. 

639 TO 470 B.C. 

Ignorance of the Greeks concerning Nature — Ionian School of Learn- 
ing — Thales — Anaximander — Pythagoras — True Sayings of Pytha- 
goras and his Followers about Geology. 

About 600 years before Christ was born, the Greeks were 
the most learned people in Europe. They were naturally 
a handsome and clever race, and their young men were 
trained to be both good soldiers and good scholars. An 
English boy, if he could be carried back to those days, 
would find that the young Greeks could read, write, draw, 
and argue as well as himself, and probably that they could 
leap, wrestle, and run better than himself or any of his 
schoolfellows. 

But on some points he would find that their ideas were 
very strange. If he spoke to them of the world as a round 
globe they would stare in astonishment, and tell him that 
such an idea was absurd, for everyone knew that the world 
was flat, with the sea flowing all round it. If he asked them, 
in his turn, about Mount Etna, they would surprise him by 
replying that the god Vulcan had his smithy underneath the 
mountain, where he was forging thunderbolts for Jove, and 
that Etna was the chimney of his forge. But if he spoke of 
the sun as a globe of light, they would turn away from him 
in horror as a wicked unbeliever in the gods, for who among 
the Greeks did not know that the sun was the god Helios, 



8 SCIENCE OF THE GREEKS. ft. i. 

who drove his chariot every day across the sky from east to 
west ? In fact, the Greeks, though learned and brave, were 
quite ignorant of what we now call ' natural knowledge ;' 
they did not know that the rising and setting of the sun, 
and the eruption of a volcano, are things which happen from 
natural causes ; but everything which was not done by man, 
they thought was the work of invisible beings or gods, 

It was not long, however, before some wise men began 
to think more deeply about these things. You will have 
read in Grecian history how the Greeks, after the taking of 
Troy, crossed over the Hellespont and founded colonies on 
the coast of Asia Minor ; one of the largest of these colonies 
was catted Ionia, and the Ionians became famous for their 
learning and wisdom. 

Thales, 640 b.c. — Here Thales, one of the seven wise 

men of Greece, was born at Miletus, about 640 b.c. Thales 

travelled in Egypt, and learned many things from the 

Egyptians, and then returned to his own land and founded 

a school of learning. He was the first Greek who studied 

astronomy, and although, like his countrymen, he believed 

that the earth was flat and floated on the water, yet he made 

several great discoveries. 

j^ The Greeks had always divided their year into two parts 

T^L^ ^-o^ .only, summer and winter, but Thales d iscovere d that there 

^X^w - are four distinct divisions m arked out b y the sun . He 

tFfijv s^&Z^J 10 ^^ tnat * n tne m iddle °f w i nt er the sun, instead of 

c^du rf^ passing overhead, reached at mid-day only a certain low 

si^ud^r^ point in the heavens, and then began to set again, so that 

the day was short and the night long. This went on for a 

few days, and because the sun stood at the same height 

every day, the name of winter solstice^ or sun-standing, was 

afterwards given to these days in the middle of winter. 

Afterwards the sun began to rise a very little higher every 



CH. i. THALES—ANAXIMANDER. 9 

day, till in three months, when winter had passed away and 
the plants and trees began to bud, the sun took exactly 
twelve hours to pass across the sky from sunrise to sunset, 
so then the day was twelve hours long, and the night also 
twelve hours ; this was called the spring equi-nox, or equal 
night, meaning that the day and night were of equal length. 
After this the sun still rose higher every day, and in three 
months more stood for some days nearly overhead at mid- 
day, thus making a long journey from sunrise to sunset, and 
causing the day to be long and the night short. This was 
the summer solstice. Then the sun began to rise less high 
every day, and in another three months there was again 
equal day and equal night — the autumn equinox had arrived. 
Finally, in another three months, the shortest day came 
round again, and the whole round began afresh. This was 
how Thales marked out the solstices and the equmoxes ; we 
still call them by the same name as he did, and you may 
watch these changes of the sun in the sky for yourself* S-~-~~ ^.sVc— 

Thales knew that the s un and stars were jiot gods , and "y*d<-'j s j*^ 
thought they were made of some fiery substanc e ; he knew, T 1 ^ ****' 
also, that the moon receives its light from the sun and reflects 
it back to us. He was very learned in mathematics, and yVjenr^/it-Uuir 
framed several propositions now found in the 'Elements of * rflr 

Euclid.' He is also said to have foretold an eclipse, and y^^" ^ 
though this has been doubted, it is now certain that he 
had sufficient data to predict such an event. 

Anaximander of Miletus, 610 b.c, the friend of 

Thales, was the next Greek who made important dis- 
coveries in science. He invented a sun -dial, by making a ^c^v. cL oX> 
flat metal plate with the hours of the day marked upon it in 
a certain order, so that a large pin, or style as it is called, 
standing in the middle of the plate, cast a shadow on the 
right hour whenever the sun shone upon it. You can 



io SCIENCE OF THE GREEKS. pt. i. 

understand that as the sun is low down in the morning, and 
gradually passes overhead during the day, it will cause the 
pin to throw its shadow in different directions at different 
hours. 
q m / - / I n this way Anaximander taught the Greeks to measure 
j . the time of day. He is also said to have been the first as- 

/^U^^ tronomer w ho understo od why we see the bright face of the 
#1 /4i^/y moon grow ing from a c rescent to a full moo n and then di- 
minishing again. To know this he must also have known 
that the moon moves round the earth every month. You 
can imitate the changes of the moon if you take a round 
stone and hold it just above your head between you and 
the sun ; you will then have its shady side towards you ; 
pass it slowly round your head, you will find that you see 
first a bright edge appearing, then more and more of the 
bright side, till when the stone is on one side of your head 
and the sun the other, you will see the whole of one side 
of the stone reflecting the sun's light — this is a full moon. 
Pass it on slowly round, and you will see this bright side 
disappear gradually till you bring it back to its old position 
between you and the sun, when it will be again dark. This 
is what the moon does every month, producing what are~ 
* J^ called the phases of the moon. Anaximander also made a 
** ^ AKnap of the world, or at least of as much of it as was known 
\ rrJCt ^ in his time. 

__ Pythagoras, one of the most celebrated of the learned 

men of Greece, is the next who told us anything about 
science. The time and place of his birth are uncertain, 
but he lived between 566 and 470 b.c. He travelled in 
Egypt, and learnt much there, and afterwards settled at 
Tarentum, in Italy, where he founded the famous sect of 
the Pythagoreans. You will read of the opinions of Pytha- 
goras in books of philosophy, but we are only concerned 
with what he taught about nature. 



ch. I. PYTHAGORAS ON GEOLOGY. M 

He was the first to assert that the earth is not fixed, but (^a^tfe ^ 
moves in the heaven s ; but he did not know that it moves > y ^t^°, 
round the sun. He also discovered that the evenin g and 
m ornin g star are the s ame pla net ; the early Greeks called / ^w^ 
tins planet Phosphorus, and it did not receive the name of 
Venus till some time afterwards. 

Some of the most rem arkable truths taught by Pyth a- . 
goras were about geology, or the study of the earth. He -^Ut^e-q/Y* 
noticed that seashells were sometimes to be found far inland * " 
imbedded in solid ground in a way that showed they were 
not brought there by man. Therefore, he argued that to 
bury j-m-shells in the rocks, the sea must once have been 
there. He had also probably watched the sea eating away 
the cliffs on the shores of Italy, as you may see it doing 
now on the shores of Norfolk and Suffolk ; and when he 
was in Egypt he must have seen the Nile carrying mud and 
laying it down at its mouth, or delta, to form new land. 
From all these and other observations he, and his pupils 
who followed him, drew some very true conclusions which 
are given in Ovid's Metci7norphoses : — 
i. Solid land has been converted into sea. 

— 2. Sea has been changed into land. Marine shells lie 
far distant from the deep. 

— 3. Valleys have been excavated by running water, and 
floods have washed down hills into the sea. 

— 4. Islands have been joined to the mainland by the 
growth of deltas and new deposits, as in the case of Antissa 
joined to Lesbos, Pharos to Egypt, etc. 

— 5. Peninsulas have been divided from the mainland and 
have become islands, as Leucadia : and according to tradi- 
tion Sicily, the sea having carried away the isthmus. 

6. Land has been submerged by earthquakes; the 
Grecian cities of Helice and Buris, for example, are to be 
seen under the sea, with their walls inclined. 



SCIENCE OF THE GREEKS. 



7. There are streams which have a petrifying power, and 
convert the substances which they touch into marble. 

8. Volcanic vents shift their position ; there was a time 
when Etna was not a burning mountain, and the time will 
come when it will cease to burn. 

These, and other sentences of the same kind, show how 
carefully Pythagoras and his followers must have observed 
nature, for the changes that are going on upon the earth 
take place so very slowly that it is only by very careful 
comparison that we can prove they are happening at all. 
Pythagoras was the first man who was called a philosopher, 
or lover of wisdom. He made many discoveries about 
musical notes, and the manner in which the different 
musical intervals can be produced on a stretched string. 
^^^JiZJ^ He was the i nvent or of a very simple but useful instrument 
0l^ syisKr*^-" called the monochor d. which consists of a sounding board 
cr-d^tr^cK * and box on which a single string is stretched, and having 
a small loose piece of wood, called a bridge, which is placed 
under the wire to divide it into segments. Pythagoras 
found that when he placed this bridge so as to divide the 
wire into two parts, of which one was twice as long as the 
other, and then struck each part, the shorter length gave a 
note of the same tone as the longer one, but at a higher 
pitch. If, however, he divided the string so that the two- 
fifths were on one side and three-fifths on the other, then 
the notes were separated by an interval of a fifth. In this 
way, by marking a scale of divisions on the sounding board, 
the Greek musicians were able to produce a whole series 
of musical notes on one string. 



ANAXAGORAS STUDIES THE MOON. 13 



CHAPTER II. 

499 to 322 B.C. 

Anaxagoras — Hippocrates — -Eudoxus — Democritus — Aristotle. 

Anaxagoras, who was the next great teacher after Pytha- 
goras, was born in Ionia about 499 B.C., but he went when 
quite young to Athens. He loved to study nature for its 
own sake, and was once heard to say that he was born to 
contemplate the sun, moon, and heavens. Although there 
were no telescopes in those days, he managed to observe 
that there were mountains, plains, and valleys in the moon. 
He believed it to be a second earth, perhaps with living 
beings in it. He did not know, as we do now, that the 
moon has no atmosphere round it, such as living beings 
like ourselves require in order to breathe. He discovered frQ-^c^*^* 
that an eclips e_o f the sun is caused by the moon com ing fifrjL- eciM*^ , 
directly between the ea rth and the sun, and an eclipse of *jl ^tfrbfi*-** \ 
the moon by t he earth coming between_ _the moon andTThe * 
sun. When the moon comes exactly between our earth 
and the sun, we see the moon's dark body pass over the 
sun, so as to eclipse or shut it out ; and when our earth 
comes exactly between the moon and the sun we cut off the 
sun's light from the moon, and see our own shadow passing 
over the moon's face, and thus we eclipse the moon. 

Anaxagoras knew that the planets Jupiter, Saturn, Venus, 
Mars, and Mercury move in the heavens, and that the stars 




14 SCIENCE OF THE GREEKS. pt. l 

do not move. He believed that all the h eavenly bod ies 
were fiery j stgjies; the sun he thought was a huge fiery 
stone as big as the Peloponnesus. He was the first 
scientific man who was persecuted for declaring boldly 
what he believed to be the truth. The Greeks were very 
angry with him for teaching that the sun was not a god ; 
so he was tried at Athens, when quite an old man, and 
condemned to death. His friend Pericles pleaded for him, 
and the sentence was changed to a fine and banishment, 
and he retired to Lampsacus, where he went on teaching 
science and philosophy till his death. 

Anaxagoras was the first Greek philosopher who taught 
that t here must be one Great Intelligence ruling over the 
universe. So that the Greeks punished as an atheist the 
man who first taught them of a Supreme God. This 
example should teach us to be very careful how we con- 
demn the opinions of others, for fear that we, like the 
Greeks, should think another wicked only because his 
thoughts are nobler than we can understand. 

Hippocrate s, 420 b.c. — While Anaxagoras was study- 
ing the heavens, another man, born about 420 B.C. in the 
little island of Cos, was studying men, and how to make 
their lives healthier and happier. Hippocrates, the Father 
of Medicine, belonged to a family of doctors and priests. 
The Greeks did not understand that illness comes to us 
because we do not know how to take care of our bodies. 
They thought that every illness was a punishment sent be- 
cause one of their gods was angry, so when they were ill 
they sent a present to the temple of ^Esculapius, the god of 
medicine, and then went to the priests of ^Esculapius to 
cure them. The ancestors of Hippocrates were all priests 
of yEsculapius, but he separated himself from the priest- 
hood and devoted his time to studying the human body, 



ch. n. HIPPOCRATES— ARISTOTLE. 15 

and finding out the causes of disease. He studied the 
effect that heat and cold have upon us, and taught physi- 
cians to pay attention to the kind of food given to sick 
people, and especially to watch carefully in sickness for the 
critical point when the fever is at its height. He wrote 
many learned works on the human body, and you should 
remember his name as the Founder of the science of 
Medicine . 

Eudoxus, 406— Democritus, 459 B.C. — The great 
astronomer after Anaxagoras was called Eudoxus. He was 
born about 406 b.c, at Cnidos, in Asia Minor, where he 
had an observatory, from which he could watch the heavens, v jgj) jJ^J* 
and by this means he ma de a map of all the stars the n ' 
known. He was the first Greek astronomer who explained 
how the planets Jupiter, etc., moved round in the heavens, 
and the time at which they would appear again exactly in 
the same place as before. The great philosopher Demo- 
critus, of Abdera (459 B.C.), who lived about the same time 
as Eudoxus, made the remarkable guess that the beautiful lAu'l^H^ 
bright band called the c .Milky Way ,' which stretches every V J <* 
evening right across the sky, is compo sed of millions of 
stars scattered Jike^djisLpver the heavens. 

Aristotle, 384 B.C., one of the most famous philo- 
sophers of Greece, was also a great student of nature. He 
was born at Stagira, in Thrace, 384 B.C., but studied at 
Athens under Plato, and afterwards became the tutor of 
Alexander the Great. Aristotle did much for astronomy, ^ ^zfc 
by collecting and comparing the discoveries of the astro- ^<rt^^ **-> 
nomers who came before him. He is the first of the Greek 
writers who states very decidedly that the earth must be a 
round globe, and he observed an eclipse (or qccultation 
as it is termed by astronomers) of the plan et Mars by the 
moon. 



A 



16 SCIENCE OF THE GREEKS. pt. i. 

But the best scientific work of x\ristotle was his study of 
anima ls. He persuaded Alexander the Great, who governed 
Greece at that time, to employ several thousand people to 
collect specimens of animals in all parts of Europe and Asia, 
and to send them to Athens. Here Aristotle examined 
them and arranged them under different classes according 
to their organs, or different parts of their body, and the 
manner in which they used them. Many of Aristotle's 
divisions of the animal kingdom are still in use, and he may 
fairly be called the Founder of Zoolo gy. He pointed out 
that we can trace an unbroken chain from the lowest plant 
up to the highest animal, each group being only divided 
from the next by very slight differences ; nor can we tell, he 
said, where plants end and animals begin, for there are some 
forms which are so like both plants and animals that we 
cannot decide in which division to place them. 

He also pointed out that the life in plants is much 
lower than in most animals ; for if you cut a plant into 
pieces, the separate pieces will often grow, showing that 
the parts of a plant are simple and do not depend very 
closely upon each other. But any one of the higher 
animals is a most complicated piece of machinery. If you 
hurt or destroy any of the most important parts the whole 
body dies, and if you cut off any part whatever, that part 
dies as soon as it is separated from the rest. These and 
many other interesting facts about animals are to be found 
in Aristotle's great work on Natural History, which, how- 
ever, you must remember, was only one out of many philo- 
sophical works written by him. 

Theophrastus, 371 B.C. — Among the pupils of Aristotle 
was a man named Theophrastus, who was born at Eresus, 
371 B.C. Theophrastus devoted himself chiefly to the 
study of plants, and is the first botanis t whose name has 



ch. ii. THEOPHRASTUS THE FIRST BOTANIST. 17 

been handed down to us. The Greeks understood very 
little about plants except those which they used for medi- 
cine; but Theophrastus described no less than 500 differ- 
ent kinds of plants, and divided them into trees, herbs, and 
shrubs. 










&-*SlsV0 



/ 



18 SCIEiVCE OF THE G REEKS. ft. l 



CHAPTER III. 

320 tO 2 12 B.C. 

School of Science at Alexandria — The Ecliptic and the Zodiac — 
Aristarchus — Euclid — Archimedes. 

While Aristotle was studying science at Athens, the Greeks 
under Alexander the Great were making great conquests in 
Egypt, where Alexander founded a city bearing his own 
name on the shores of the Mediterranean. After Alex- 
ander's death this city, called Alexandria, fell to the portion 
of Ptolemy Lagus, one of Alexander's generals, who was 
succeeded by a number of princes of the same name. The 
Ptolemies were all patrons of learning and science, and the 
school of Alexandria became one of the most famous the 
world has ever known. By this time the Greeks had learnt 
many astronomical facts, some of them probably from the 
Egyptians. They had traced the ecliptic, or the sun's appar- 
ent yearly path through the heavens, and, dividing this path 
into twelve parts, they called each division by the name of 
a constellation or cluster of stars. These constellations re- 
ceived most of them the names of animals, and therefore 
the circle of the twelve constellations was called the Zodiac, 
or circle of animals. The names of the twelve signs are : 
1. Aries, the Ram; 2. Taurus, the Bull; 3. Gemini, the 
Twins ; 4. Cancer, the Crab ; 5. Leo, the Lion j 6. Virgo, 
the Virgin ; 7. Libra, the Balance ; 8. Scorpio, the Scorpion; 



ch. in. SIGNS OF THE ZODIAC. 19 

9. Sagitta?'ius, the Archer; 10. Cafiricornus, the Goat ; n. 
Aquarius, the Water-bearer; 12. Pisces, the Fishes. 

It was by no means an easy thing to trace the sun's path 
among the stars, because the sun and the stars are never in 
sight at the same time, so astronomers were obliged to notice 
the constellations as they appeared close to the sun after 
he sank at night or before he rose in the morning. These, 
they found, varied a little each night, till when a whole 
year had passed away, each of the twelve signs had been 
in turn close to the sun, and the round began again. Thus 
they learned that the sun passed over each of the twelve 
signs in the course of the year ; and they thought from this 
that the sun travelled round the sky while the earth stood 
still in the middle. We know now that it is the sun which 
stands still in the middle while the earth moves round, and 
it is worth while to make an experiment to see how the 
Greeks were deceived. 

Put twelve chairs round in a circle to represent the 
signs of the Zodiac, and put yourself in the middle for a 
person standing on the earth. Then swing a ball round you 
just on a level with the chairs. You will see that the ball 
passes between you and each chair as it makes a circle round 
you. The Greeks believed that the sun moved round in 
this way between us and the stars. But now to represent 
what really takes place, change places with the ball. Hang 
the ball (the sun) up in the middle just on a level with the 
chairs, and walk round it. Keep your eye fixed on the ball, 
and you will see it will pass between you and each chair, 
just as it did before. The effect is the same, though it is 
you who are moving this time and not the ball. Thus the 
Greeks made the same mistake which a child does in a rail- 
way train when he thinks the houses and trees are flying 
past, while it is really he himself who is moving. 
3 



20 SCIENCE OF THE GREEKS. PT. I. 

Aristarehus. — There was, however, one Greek astrono- 
mer named Aristarehus, who discovered the real movement 
as we know it now. Aristarehus was born in Samos, some 
time in the third century before Christ, but he came to Alex- 
andria, and was tutor to the sons of one of the Ptolemies. 
^^vj L^uH Hq taught that the s un was immovab le like the fixed stars, 
\j<r^k\ and that it was the earth which travelled round the ecliptic. 

t He knew also that our earth does not stand quite upright in 

>Jfi^ c f its journey round the sun, but that a line drawn through the 
'}/> . earth from the north to the south pole would be sloping or 

oblique to the ecliptic, and that this obliquity is the cause of 
our four seasons. 

If you do not understand this you can work it out with 
your ball, using a lamp to represent the sun. First draw an 
ink-line round the middle of your ball for the equator, then 
put your finger and thumb at the two ends of the ball to 
represent the two poles. Do not hold the ball upright, but 
bring your thumb nearer to you than your finger. A line 
drawn through the ball from your finger to your thumb will 
now be ificlined, and will represent the inclined axis of the 
earth. Now look at the light and shade on the ball : the 
north pole, which is turned towards the lamp, will be in full 
light, and will have the long days of summer ; the south 
pole turned towards you will be in the dark, enduring its 
long winter night. Pass the ball on to your right, and when 
you have gone round a quarter of a circle the poles will 
both have equal light, and the southern spring and northern 
autumn have arrived. Pass on again, and at the next 
quarter the south pole will be in summer and the north pole 
in winter, while at the fourth and last point you have the 
northern spring and the southern autumn. This was what 
Aristarehus discovered, namely, that the changing seasons 
are entirely caused by the earth having its axis (or the line 



CH. in. EUCLID AND ARCHIMEDES. 21 

from pole to pole), oblique to its path round the sun, called 
the ecliptic. This is called the obliquity of the ecliptic. 

Aristarchus appears also to have been the first Greek 
who understood that day and night are caused by the ear th <y^^ *c 
turning round on its avis fvpry day. If the Greeks had J 
understood his teaching, especially about the earth moving 
round the sun, they would have made much more progress 
in astronomy. But no one believed him, and more than 
1700 years passed away before Copernicus, of whom we 
shall speak in Chapter IX., discovered this great truth over 
again. This Greek theory of the earth moving round the 
sun is often called the Pythagorean system, for it was 
thought that Pythagoras taught it ; but we have seen that, 
though Pythagoras knew that the earth moves, he did not 
believe that it went round the sun. 

Euclid, 300 b.c. — We must not pass through the third 
century before Christ without mentioning Euclid, the great 
mathematician and geometer, who collected together the 
propositions in the ' Elements of Euclid,' known to every 
schoolboy. He was born at Alexandria about 300 B.C. t/ . 

His works are too difficult for us to examine, and the only ^^7^ 
discovery of his we can mention is, t hat light travels i n ^^ 
s traight lines called * rays / Thus, if you look at a sun- 
beam shining across a dusty room, you can see the light 
reflected in a straight line along the particles of dust, and if 
you let sunlight through a hole in the shutter into a dark 
room, it will light up a spot on the wall or floor exactly 
opposite to the sun ; — the middle of the sun, the middle of 
the hole in the shutter, and the middle of the spot of light, 
will all be in a straight line. 

Archimedes, 287 B.C. — Another famous geometer, 
Archimedes of Syracuse, born 287 B.C., lived about the 
same time as Euclid. He studied for many years at 



I. 



22 SCIENCE OF THE GREEKS. ft. i. 

« a Alexandria, but afterwards returned to his native country. 

j^C^vt^MT Q ne f the greatest discoveries made by Archimedes was that 

I of the principle of the leve r. If you place a book upright on 

the table and lay a light ruler or flat piece of wood across 

? * cA-^-v it> y° u wn ^ fi R d there is one point at which the ruler will 

h balance. When you have balanced it, put an ounce weight 

on each end and it will still balance at the same point, 

which is called the fulcrum. But now change the ounce 

at one end for a weight of two ounces ; that end will sink 

at once, and to make it balance you will have to shift the 

ruler till one end is longer than the other. You may go 

on doing this by adding more weight to the heavy end till 

that end is quite close to the fulcrum or resting-point of the 

ruler, and still the light weight will balance the heavy one. 

This is the principle of the lever, and it is of great use 
in lifting weights. A heavy block of stone which no set of 
men could lift by taking hold of it may be easily raised by 
fastening it to the short end of a lever, and then the weight 
of the men at the end of the long arm will balance it, as 
the one-ounce weight balances the heavier weights at the 
other. Archimedes was so delighted when he made this 
discovery that he is said to have exclaimed : ' Give me a 
place on which to stand, and I will raise the world.' 

Another remarkable discovery made by Archimedes con- 
cerns the weight of bodies immersed in water. Hiero, king 
of Syracuse, had given a lump of gold to be made into a 
crown, and when it came back he suspected that the work- 
men had kept back some of the gold, and had made up the 
weight by adding more than the right quantity of silver; 
but he had no means of proving this, because they had 
made it weigh as much as the gold which had been sent 
Archimedes, puzzling over this problem, went to his bath. 
As he stepped in he saw the water, which his body dis- 



ch. in. HIERCfS CROWN. 23 

placed, rise to a higher level in the bath, and to the 
astonishment of his servants he sprang out of the water 
and ran home through the streets of Syracuse almost naked, 
crying Eureka ! Eureka ! (' I have found it, I have found 

if). * 

What had he found? He had discovered that any 
solid body put into a vessel of water displaces a quantity 
of water equal to its own bulk, and therefore that equal 
weights of two substances, one light and bulky, and the 
other heavy and small, will displace different quantities of 
water. This discovery enabled him to solve his problem. 
He procured one lump of gold and another of silver, 
each weighing exactly the same as the crown. Of course 
the lumps were not the same size, because silver is lighter 
than gold, and so it takes more of it to make up the 
same weight. He first put the gold into a basin of water, 
and marked on the side of the vessel the height to which 
the water rose. Next, taking out the gold, he put in the 
silver, which, though it weighed the same, yet, being larger, 
made the water rise higher ; and this height he also marked. 
Lastly, he took out the lump of silver and put in the crown. 
Now, if the crown had been pure gold, the water would 
have risen only up to the mark of the gold, but it rose 
higher and stood between the gold and silver mark, show- 
ing that silver had been mixed with it, making it more 
bulky ; and, by calculating how much water was displaced, 
Archimedes could estimate roughly how much silver had 
been added. This was the first attempt to measure the 
specific gravity of different substances, that is, the weight of 
any particular substance compared to an equal bulk of some 
other substance taken as a standard. In weighing solids 
or liquids water is the usual standard. 

It will be quite sufficient if you remember the experiment 



24 



SCIENCE OF THE GREEKS. 



PT. I. 



as I have explained it ; but as you may perhaps be puzzled 
to see how it can have anything to do with weight, it will 
be well to try to master the following explanation of Fig. i, 
which shows how specific gravity is measured. You must 
begin by remembering that the crown, the gold lump, and 
the silver lump, when weighed in the air, will all pull the 
marker of the spring balances a, b, c, down to 1 9 ; that is, 




Fig. i. 

Diagram showing the difference of specific gravity between equal weights of gold, 

silver, and mixed metal. 
ABC, Spring balances, d, Gold ball weighing 19 02. e, Silver ball weighing 19 oz. 

/, Crown of mixed metal weighing ig oz. 

they will all weigh 19 ounces. Bat when they are immersed 
in water they will no longer weigh the same, because the 
water round them buoys them up just as much as it would 
buoy up the quantity of water which they displace. 



CH. in. ARCHIMEDES— SPECIFIC GRAVITY. 2$ 

Now, the gold takes the place of as much water as would 
weigh one ounce if you could take it out and weigh it in the 
air. So it is buoyed up one ounce by the water round it, 
and accordingly you see it only pulls the marker down 18 
ounces instead of 19. But the silver, although it weighs 
the same, is larger, and takes the place of nearly two ounces 
of water, therefore it is buoyed up nearly two ounces, and 
only pulls the marker down to 17. Now, as the crown 
weighs the same as either of the two lumps, its shape is of 
no consequence \ if it was made all of gold it would take 
as much room, and be buoyed up as much as the gold. If 
it was all silver it would be buoyed up as much as the silver, 
and therefore, as it pulls the marker down half-way between 
1 7 and 1 8 ounces, it must be half gold and half silver. 

In this way Archimedes showed how we can learn the 
weight of any solid compared to an equal bulk of water, 
and this is called the ' specific gravity ' of the substance. 

He also invented a screw for pumping up water, which 
is still called the ' screw of Archimedes.' 

Archimedes was unfortunately killed in the city of Syra- 
cuse when it was besieged by the Romans during the second 
Punic war. The Roman general Marcellus had given 
special orders that his life should be spared ; but he was so 
deeply engaged in solving a problem that he heard nothing 
of the din of war around him, and a common soldier not 
being able to get any answer from him, killed him without 
knowing who he was. 



26 SCIENCE OF THE GREEKS. ft. I. 



CHAPTER IV. 

28o TO I20 B.C. 

Erasistratus and Herophilus — Eratosthenes — Hipparchus — Precession 
of the Equinoxes. 

Erasistratus and Herophilus.— At the time when Archi- 
medes was studying in Alexandria, two physicians were 
teaching there, who are famous in the history of anatomy, 
or the structure of the body. The one was Erasistratus 
and the other Herophilus. The birthplaces and dates of 
these two physicians are doubtful, but we know that they 
were the first men who dissected the human body, and gave 
a clear account of its parts. Erasistratus, in particular, 
described the brain and its curious windings or convolutions, 
and the division between the cerebrum or front part and 
the cerebellum or hinder and lower part. He seems also 
to have known that it is by means of our brain that we feel 
everything, and that it is the nerves which carry messages 
from different parts of our body to our brain. Herophilus 
traced out the tendons or strong cords which fasten the 
muscles to the bones ; the ligaments or fibrous cords which 
unite one bone to another ; and the nerves. He was the 
first physician who pointed out that in feeling a pulse you 
must notice three things: 1 st, how strongly it throbs ; 2d, 
how quickly ; 3d, whether the beats are regular or irregular. 
Many of the names which Erasistratus and Herophilus gave 



/ 









™ ^^J^uJJ^ W ^ 






ch. iv. ERATOSTHENES— PARALLEL OF LATITUDE. 27 

to parts of the body are still used by anatomists, and the 
school of medicine founded by them in Alexandria was 
renowned for more than six hundred years. 

Eratosthenes, 276 B.C. — We must now turn to the 
science of geography, which at this time began first really 
to be studied by a Greek named Eratosthenes, born at 
Cyrene 276 B.C. Like all men of science of that day, he 
too came to Alexandria, where the king, Ptolemy Euergetes, 
made him keeper of the Royal Library. He made a map / 
of ^ *h f^ world that was then known, and described the 
countries of Europe, Asia, and Libya; but he is chiefly *2- 
famous for having laid down the first parallel of latitud e, and 
trying to measure the circumference of the earth. He laid 
down the parallel of latitude in the following manner. He 
knew that at all places on the equator the day was exactly 
the same length all the year round, and that the length of 
the days and nights varied more and more as you went 
northwards ; therefore he reasoned that, if he could draw a 
line east and west through a number of places whose longest 
day was exactly the same length, those places would all be 
at the same distance from the equator. Lie began at the 
Straits of Gibraltar, where the longest day was exactly 14^ 
hours, and then observing all those places whose longest day 
was also 14J hours, he drew a line through the south coast 
of Sicily, across the south of the Peloponnesus, the island of 
Rhodes, the bay of Issus,and across the Euphrates and Tigris, 
out to the mountains of India. If you follow this line on 
a map you will find it is the 36th parallel of north latitude, 
and that Eratosthenes' observation was perfectly correct. 

This discovery led him on to try and measure the cjr- 3 
cumference of the earth y Having found a line straight 
round the earth from east to west, he knew that if he drew 
a line at' right angles to it, that is exactly north and south, 



28 SCIENCE OF THE GREEKS. PT. I. 

he should have a line which would describe a circle round 
the earth from pole to pole, as the equator marks a circle 
round the earth midway between the two poles. This 
second line he drew from Alexandria, and it passed right 
through Syene, now called Assouan, one of the southern 
cities of Egypt ; and thus he knew that Alexandria and 
Syene were on the same meridian of longitude. 

Now he found that at Syene the sun was exactly over- 
head at mid-day, at the time of the summer solstice. He 
knew this by means of a gnomon, or upright pillar (b, Fig. 2), 
which was used by the Greeks to measure the height of the 
sun in the sky. At Syene this pillar cast no shadow at noon 
of the summer solstice, proving that the sun shone straight 
down upon the top of it ; and this was further proved by 
the sun shining down to the bottom of a deep well, which 
it would not do unless it were directly overhead. But at 
Alexandria the gnomon did cast a shadow, because, as 
Alexandria was farther north and the earth is round, the 
sun there was not directly overhead. Now, as light travels 
in straight lines (see p. 21), a line drawn from the extreme 
point of the shadow cast by the pillar or gnomon up to the 
top of the pillar itself would, if carried on, run straight into 
the sun, and thus the angle between this line and the pillar 
showed at what angle the sun's rays were falling at Alex- 
andria. By measuring this angle, Eratosthenes found that 
Alexandria was -gVth of the whole circumference of the earth 
north of Syene, where the rays were perpendicular. 

You can form an idea of this from the accompanying 
diagram, Fig. 2. Let the large circle represent the earth ; 
b the gnomon at Syene, and a the gnomon at Alexandria. 
The length of the shadow c d of the gnomon a, will bear the 
same proportion to the circumference of the small circle 
(drawn from the top of the gnomon as a centre), that the 



CH. IV 



CIRCUMFERENCE OF THE EARTH. 



29 



distance from Alexandria to Syene (d to e) does to the 
whole circumference of the globe. This is true only if the 
rays from the sun to Alexandria and to Syene are parallel 
(or run at equal distances). 
They are not really quite 
parallel because they meet 
in the sun, but Eratosthenes 
knew that the sun was at 
such an enormous distance 
that their approach to each 
other was quite unimport- 
ant. He now measured 
the distance between Alex- 
andria and Syene, and found 
it to be 5,000 stadia, or 
about 625 miles, and mul- 
tiplying this by 50 he got 
625 x 50 = 31,250 miles 
as the whole circumference 
of the earth, measured 
round from pole to pole. This result is not quite correct, 
but as nearly as could be expected from a first rough 
attempt. 

Eratosthenes also studied the direction of mountain- 




FlG. 2. 

Diagram showing how Eratosthenes mea- 
sured the circumference of the earth. 

A, Gnomon at Alexandria. B, Gnomon at 
Syene. cd, Length of shadow of gnomon. 
D e, Distance from Alexandria to Syene. 



chains, th e way in which clouds carry rain, the shape of the 
continents, and many other geographical problems. 

Hipparcrms, 160 B.C. — Nearly one hundred years after 
Eratosthenes, the great astronomer Hipparchus was born, 
160 b.c. Hipparchus was the most famous of all the astro- 
nomers who lived before the Christian era. He collected 
and examined all the discoveries made by the earlier obser- 
vers, and made many new observations; but astronomy had 
now become so complicated that the problems are too diffi- 




30 SCIENCE OF THE GREEKS. pt. i. 

cult to be explained here. Hipparchus was supposed to 
have made a c atalogue of 1080 s tars, but recent researches 
seem to prove that these were made later by Ptolemy. He 
also calculated accurately when eclipses of the sun or the 
moon would take place. But his great discovery was that 
called the ' Precession of the Equinoxes.' This is a very 
complicated movement not easy to understand ; but I will 
try to give a rough idea of it, in order that you may always 
connect it with the name of Hipparchus. 

We have seen that the earth has two movements — one, 
turning on its own axis causing day and night ; the other, 
travelling round the sun, causing the seasons of the year. 
But besides these it has a third curious movement, just like 
a spinning-top when it is going to fall. Look at a top a 
little while before it falls, and you will see that, because it is 
leaning sideways, the top of it makes a small circle in the 
air. Now our earth, because it is pulled at the equator by 
the sun, moon, and planets, makes just such a small circle 
in space ; so that, instead of the north pole pointing quite 
straight to the polar star, it makes a little circuit in the sky, 
with the polar star in the centre. The pole moves very 
slowly, taking twenty-one thousand years to go all round 
this circle. To understand the effect of this movement we 
must examine more closely what the equinoxes are. Take 
your ball again and make it go round the lamp with its 
axis inclined (see p. 20). When you have it in such a posi- 
tion that the north pole is in the dark, or the northern 
winter solstice, you will find that a straight line drawn from 
the sun to the centre of the earth will not meet the equator 
but a point to the south of it. But now pass the ball on to 
the next point when neither pole is in shade, and when it is 
equal day and equal night over the globe (our spring equi- 
nox), a line now drawn from the sun will fall directly upon 



ch. iv. PRECESSION OF THE EQUINOXES. 31 

the equator, so that the sun's path meets the equator at 
this point, which is called the equinoctial point. Pass on 
till the south pole of your ball is in the dark, the sun will 
now fall directly on a point north of the equator (making our 
summer solstice). Pass on again to the point of equal day 
and equal night, and the sun again falls direct on the equa- 
tor, causing our autumn equinox. Now, if the earth did not 
make that small circle in space like the top, the sun would 
always touch the equator at exactly those same points of 
the earth's orbit or path round the sun ; but the effect of 
that movement is to pull the equator slightly back, so that 
the points where the ecliptic and the equator cut each 
other are 50} seconds more to the west every year, and in 
this way the equinoxes would travel all round the orbit from 
east to west in about 26,000 years were it not that a gradual 
change in the direction of the major axis of the earth's 
orbit, known as " the revolution of the apsides," shortens 
the period and reduces it to 21,000 years. Hipparchus 
discovered this precession (or going forward) of the equi- 
noxes ; though he did not know, what Newton afterwards 
discovered, that it is caused by the sun and moon pulling 
at the mass of extra matter which is gathered round the 
equator. 



32 SCIENCE OF THE GREEKS. ft. 



CHAPTER V. 

FROM A.D. 70 TO 200. 

Ptolemy — Ptolemaic System — Strabo — Pliny — Galen — Greece and her 
Colonies conquered by Rome — Decay of Science in Greece — Con- 
cluding Remarks on Greek Science. 

Ptolemy, a.d. 100. — After Hipparchus there were many 
good astronomers at Alexandria, but none whom we need 
notice until the period from 100 to 170 after Christ, when 
Claudius Ptolemy, the great astronomer, flourished. Claudius 
Ptolemy was a native of Egypt He was not one of the 
Ptolemies who governed Alexandria, and the place and date 
of his birth are unknown, but he is famous for having made 
a regular system of astronomy founded upon all that the 
Greeks had learnt about the heavens. His discoveries, like 
those of Hipparchus, are too complicated for us to discuss 
here ; they related chiefly to the movements of the moon 
and the planets ; but the one great thing to be remembered 
of him is, that he founded what is called the Ptolemaic Sys- 
tem of astronomy, which tries to explain all the movements 
of the sun, stars, and planets, by supposing the earth to 
stand still in the centre of them all. This system is con- 
tained in Ptolemy's great work called 'The Almagest.' It may 
seem strange that as it is not true that the earth is the centre, 
Ptolemy should have been able to explain so much by his 
system, but you must remember that it had the same effect 



CH. v. PTOLEMY, STRABO, AND PLINY. 33 

whether you moved round the ball, or the ball round you, 
in our experiment on page 19 ; and Ptolemy's explanations 
were apparently so near the truth that astronomers were 
satisfied with them for 1400 years, till Copernicus discovered 
the real movements. 

Ptolemy was a geographe r as well as an astronomer ; 
he wrote a book on geography which was used in all the 
schools of learning for nearly fourteen hundred ye ars. He 
drew maps of all the known parts of the world, and laid 
down on .them lines of latitude and longitude, which he 
calculated by the rules Eratosthenes had discovered. In 
his geography he describes the countries from the Canary 
Islands on the west to India and China on the east, and 
from Norway to the south of Egypt. He describes our 
island under the name of Albion, or Britain, and traces out 
many of the coast-lines and rivers. He also gives the names 
of the various towns, with their latitude and longitude. 

Strabo and Pliny.— Between the beginning of our era 
and the time of Ptolemy there lived two remarkable men 
who require a passing mention. The first of these was a 
famous traveller named Strabo, who wrote a great d eal on 
geography. He was born at Amasia, in Cappadocia, and 
was probably living when Christ was born. Strabo in his 
book describes the countries which he visited and read 
about. He also studied earthquakes and volcanoes, and 
pointed o ut that when the h ot vapo ur and lava hidden in 
the crust of our earth can not esca pe, they cause earth - 
q uake s, but that when they find their way out through a 
volcano, like Etna, the country is not so often disturbed 
and shaken. The second of these men, Pliny, the famous 
naturalist, was born a.d. 23, and died in the year 79 in a 
rash attempt to approach Vesuvius during the celebrated 
eruption which overwhelmed Herculaneum and Pompeii. 



34 SCIENCE OF THE GREEKS. PT. I. 

Pliny wrote much on Natural History, but he did not make 
many original observations. 

Galen, 131.— There is still one more great man of 
science whom we must mention as having studied at the 
Greek school at Alexandria. This was Galen, one of the 
most celebrated physicians of antiquity. He was born a.d. 
131, at Pergamos, in Asia Minor, where he received a 
liberal education, comprising all the branches of science 
known to the Greeks. He then turned his attention to 
medicine, and travelled to Smyrna, Corinth, and Alexandria. 
After practising for some time in his native country he went 
to Rome, where he became very famous. During his life 
he is said to have written more than 500 valuable _essays 
on medici ne and the h uman bo dy. You will remember 
that Erasistratus and Herophilus dissected the human body ; 
but in the time of Galen this seems to have been forbidden, 
and he was obliged to work upon monkeys and other 
animals. Even from these, however, he learnt some very 
important facts. For instance, he discovered the difference 
between the two sets of nerves which we have in our body, 
called the nerves of sensation and the nerves of motion. 

Our bodies are provided with two sets of fine cords or 
threads called nerves ; one set running from different parts 
of the body to the spine and the brain, and the other set 
running back from the spine and brain to the body. If 
you touch a hot iron with your finger, the nerves of sensa- 
tion, that is, of feeling, carry the message to your brain 
that the iron is hot, and then instantly the nerves of motion 
carry the message back from your brain to your finger, and 
you snatch it away. If the nerves between your finger and 
your brain had been cut or injured you would not feel pain 
when you touched the hot iron, nor draw your finger away. 
You will remember that Erasistratus had an idea that it is 




^^^^Z^c^feZ^ , 



*^~^t/-a~L. t?C* 











^^ 



2^ 



^K 






/fcm 



^C^CJ 




/ CisisltX' 



ch. v. CONCLUDING REMARKS. 35 

in our brain that we feel ; Galen proved this by many ex- 
periments, though he did not understand clearly the whole 
action of the nerves. He also proved that the veins of our 
body contain blood, and he described the two muscles 
which by their contraction pull down the lower jaw as we 
open and pull it up as we shut our mouths. Besides these 
and many other discoveries, Galen worked out a whole 
theory of medicine, and how doctors were to treat their 
patients, and his rules were the guide of physicians for 
many hundred years. 

Concluding Remarks on Greek Science.— We have 
now come to an end of the science of the Greeks. You 
will read in Grecian history how Greece and the Greek 
colonies were conquered by the Romans more than a 
hundred years before Christ was born ; and when the 
Greeks ceased to be a free people they gradually lost their 
love of discovery and of science. The school at Alexandria 
continued to be famous for many centuries after Christ, 
but the professors who taught there only repeated the say- 
ings of Ptolemy, Aristotle, Galen, and the other great dis- 
coverers, and did not find out new facts for themselves ; 
and at last, in the year 640 after Christ, the Arabs took 
possession of the city, and it soon ceased altogether to be 
Greek. 

You must remember that in these five chapters we have 
only been able to speak of some of the greatest men, and 
then only of a few of the discoveries they made. You will 
hear of many celebrated Greek philosophers, as, for example, 
Socrates and Plato, whose names are not mentioned here 
because they taught on subjects such as the mind and the 
soul, which belong to higher philosophy, and not to Natural 
Science. You will also hear of many strange and absurd 
notions about the causes of things which in those early 



36 



SCIENCE OF THE GREEKS. 



FT. I. 



days were held, even by such men as Pythagoras or Galen ; 
but in this book we have only to try to understand the real 
facts which have been discovered ; and there is no doubt 
that the Greeks, by a patient study of nature, and by making 
real and careful observations and experiments, laid the found- 
ations of much of the knowledge which we have carried 
so much farther in modern times. The moment they began 
merely to repeat the teachings of others, instead of trying 
and proving the truth of them, they made no more discov- 
veries, but lost a great deal they had gained. For a mere 
reading of books will not teach science ; and if you admire 
these men for making great discoveries, and would like to 
be a discoverer yourself, you must not be content with 
knowing what has been done, but must set to work as they 
did, and observe and make experiments for yourself. 



Chief Works consulted. — Draper's 'Intellectual Development in 
Europe ;' Lewis's ' Astronomy of the Ancients ;' ' Encyclopaedia Bri- 
tannica,' art. 'Astronomy;' Herschel's 'Astronomy;' Baden Powell's 
'History of Natural Philosophy;' Lardner's 'Cyclopaedia,' 1834; 
Sprengel's ' Histoire de la Medecine,' 181 5 ; Grant's 'History of 
Physical Astronomy;' Lange's ' Geschichte des Materialismus ; ' Rees* 
* Encyclopaedia ;* Whewell's ' History of Inductive Sciences. 5 



PART II. 

SCIENCE OF THE 
MIDDLE OR DARK AGES 

6, /*cuU <*/ tZty^L^. /W?t'^ 



«L ' 





^^^cj^tx*- u^t^ j^usOus 



2T2 






Chief Men of Science in the Middle Ages. 



LAA-^* > lA , * , * 








A.D. 


Marcus Grsecus .... 800. 


Geber or Djafer 








83O. 


Albategnius . 








879. 


Ben Musa . 








900. 


Avicenna 








98O. 


Gerbert 








IOOO. 


Eben Junis . 








IOO8. 


Alhazen 








IOOO. 


Roger Bacon 








1214. 


Vitellio 








1220. 


Flavio Gioja 








1300. 


Columbus . 








1435. 


Vasco de Gama 








1450. 


Ferdinand Magelk 


m 






1470. 


Leonardo da Vine 


L 






. 1452. 



ch. vi. SCIENCE OF THE ARABS. 39 



CHAPTER VI. 

SCIENCE OF THE ARABS. 

Dark Ages of Europe — Taking of Alexandria by the Arabs — The 
Nestorians and Jews translate Greek works on Science — Univer- 
sities of the Arabs — Hermes the first Alchemist — Gases and Vapours 
called ' Spirits ' by the Arabs. 

Arabian Science. — We have now arrived at what have 
been called the ' Dark Ages/ because for several hundred 
years Europe was too much engaged in wars and disputes 
to pay any attention to learning or science. You have, no 
doubt, read in history how the Goths and Vandals, a barbar- 
ous people from north-eastern Asia, spread themselves over 
Europe, conquering the Romans, and taking possession of 
all their colonies. They even crossed over into Africa, but 
were driven out again by the famous general Belisarius, in 
the reign of Justinian. This was in a.d. 534, and the 
Emperors of Constantinople held Alexandria for about 
one hundred years, and then came the Arabs or Saracens, 
pouring out of Arabia, and they took possession of Alex- 
andria in a.d. 640, only seven years after the death of their 
great leader Mahomet. 

This people, who were originally a shepherd race in Arabia, 
seemed at first to think of nothing but making themselves 
masters of new lands. They went on conquering and 
destroying till they had overrun all the north of Africa up 
to the Straits of Gibraltar, had taken possession of a great 



40 SCIENCE OF THE MIDDLE AGES. pt. n. 

part of Spain, and even of the south of France as far as the 
river Aude, in Languedoc, and then when Charles Martel, 
mayor of the Franks, conquered them at Tours in 732, and 
stopped them from going any farther, they settled down and 
began to give their attention to science and learning. 

The Arabs, however, had not only made conquests in 
the west, they had also become masters in Asia, where two 
classes of people taught them the science of the Greeks. 
These were the Nestorians and the Jews. The followers 
of Nestorius, the banished Patriarch of Constantinople, had 
migrated early in the fifth century into Asia, and founded 
there the large sect of Nestorians among the people of Assyria 
and Persia. Under the Mahommedan Kaliphs these Nes- 
torians translated many Greek works of science into Syriac 
and Arabic, and, together with those Jews who took refuge 
in Syria and Mesopotamia after the fall of Jerusalem, they 
founded several medical schools. The Arabian s chool s of 
Bagdad , Cairo, S alerno in the south of Italy, and Cordov a 
in Spain, soon became famous all over the world. The 
Arabs were not able to practise anatomy, because the 
Koran, that is the Mahommedan Bible, taught that it 
was not right to dissect the human body, so they turned 
their attention chiefly to medicine, trying to discover what 
substances they could extract from plants and minerals, at 
first to serve as medicines, but soon for very different uses. 

Arabian Alchemists. — They found something in the 
old Greek writings about the way to melt stones or minerals, 
so as to get out of them iron, mercury, and other metals ; 
and also how to extract many beautiful colours out of rocks 
and earths. But the chief thing which interested them in 
the books of the Egyptians, Chaldeans, and Greeks, was the 
attempts these nations had made to turn other metals into 
gold, a discovery which tradition said had been made by 



ch. vi. ARABIAN ALCHEMISTS. 41 

Hermes Trismegistus about 2000 years before Christ. We 
know very little of this Hermes, and indeed we are not sure 
whether he is not altogether an imaginary person ; but the 
Alchemists, as the people were called who tried to make 
gold, considered themselves followers of Hermes, and often 
called themselves Hermetic philosophers. To melt the mouth 
of a glass tube so as to close it was called securing it with 
1 Hermes, his seal,' and even to this day a bottle or jar 
which is closed so that it is air-tight is said to be hermeti-/ 
cally sealed. 

The Arabs were a very superstitious people, and believed ^ 
in all kinds of charms ; and this idea of making gold in a v 
mysterious way took a great hold of them. Many thousands 
of clever men occupied themselves in the supposed magic 
art of alchemy. We need not study it here, but only observe 
how very useful it was in teaching the first facts of chemistry. 
These men, who were many of them learned, clever, and 
patient, spent their lives in melting up different substances 
and watching what changes took place in them. In this 
way they learnt a good deal about the materials of which 
rocks, minerals, and other substances are made. 

One of the first things they discovered was that, by 
heating substances, they could often drive something out of 
them which was invisible, and yet that they could collect this 
invisible something in bottles; and in some cases if they put 
a light to it, it exploded violently, breaking the bottle to 
atoms. Now because this was invisible, and yet so power- 
ful, they thought it must be like the spirit of man, which 
can do so much and yet cannot be seen, and for this reason 
they called it ' spirit.' We know now that when we heat 
substances up to a certain point we drive apart the matter of 
which they are made, and it floats off as steam or gas into the 
air; so that this spirit noticed by the Arabs was vapour or gas. 



4 2 



SCIENCE OF THE MIDDLE AGES. 



It seems almost certain that the Arabs knew a great deal 
about gunpowder and some other mixtures which explode 
when they are set on fire. Marcus Grsecus, a man whose 
origin is unknown, but who lived about the beginning of the 
ninth century, says that if you mix together one pound of 
sulphur, two of charcoal, and six of saltpetre, it will explode 
when you light it and drive things into the air. This is 
one of the ways in which gunpowder is still made. 










^ 




CA-Ot* 









ch. vii. CHEMISTRY OF GEBER. 43 



CHAPTER VII. 

SCIENCE OF THE ARABS (CONTINUED) 

Geber, or Djafer, the Founder of Chemistry — Arabs mix up Astronomy 
with Astrology — Albategnius — Mohammed Ben Musa first Writer 
on Algebra — Alhazen's Discoveries in Optics. 

Geber's Discoveries in Chemistry, 800-900. — The 

greatest of the Arabian alchemists was a man named Geber, 
or Djafer, who was born in Mesopotamia about a.d. 830. 
He has been called the ' Founder of Chemistry,' for though, 
like his countrymen, he spent much of his time in trying to 
make gold, yet he is the first who, as far as we know, made 
really useful chemical experiments. 

He explains in his works many of the method s we now 
use in chemistry. For example, he states that if you boil 
water, the vapour (or spirit as he calls it) will rise up, and 
you can collect it and cool it down again in another vessel ; 
and it will then be pure, because any solid matter such as 
sand or salt, which does not turn readily into vapour, will 
remain behind in the first vessel. Again, if you heat wine 
or brandy gently, a vapour called alcohol or spirits of wine 
will rise up, because the alcohol turns into vapour more^f * 
easily than the other materials of the wine. If you collect 
and cool down this vapour in another bottle, you will have 
liquid spirits-of-wine. This process is called distillation, 
and is used by chemists to separate substances which turn 
readily into vapour, from others which do not boil so easily. 
4 



44 SCIENCE OF THE MIDDLE AGES. pt. ii. 

You can distil vapours from solid things as well as from 
liquids : if you heat sugar over a fire, it will soon boil, and a 
vapour will rise up from it. 

But if you put a piece of camphor in a flask with a 
stopper to it, and heat it very gently either by placing it in 
the sun or at some distance above a lighted candle, the cam- 
phor will gradually disappear from the bottom of the flask, 
and will collect again in little crystals on the inside of the 
neck. This is because camphor at an ordinary heat changes 
at once into a dry invisible gas, without first remaining 
liquid for a time as ice does. The process by which sub- 
stances are turned directly from a solid state into a dry gas 
-__is_ called sublimation ,, and Geber describes it in his book as 
'the elevation of dry things by fire.' He knew that if you 
take a kind of stone called cinnabar, and heat it, a dry gas 
rises from it, which you can collect, and which cools down 
into drops of mercury or quicksilver. 

Geber made another remarkable experiment, though he 
did not thoroughly understand it. He states in his book 
that if you take a certain weight, say a pound of iron, lead, 
or copper, and heat it in an open vessel, the metal will weigh 
more after it has been heated than it did before, which 
seems very strange, as we cannot see that anything has been 
added to it. We shall learn the reason of this when we come 
to the discoveries of Priestley (Chap. XXVII.) ; but Geber 
b carefully noticed the fact, though he could not explain it. 

I'p^J^ The discovery, however, which most of all gives Geber 
Vt^y^ Vthe right to be called the 'founder of chemistry' was that 

^\ °*" stron S acids. Most of the chemical experiments we 
^r\]^y make now would be impossible without acids, but before 

<y Geber's time vinegar seems to have been the strongest acid 

known. He found, however, that by hejuungj^rjeras (or 
sulphate of iron) with saltpetre and alum, he could distil off 



ch. vii. GEBER DISCOVERS ACIDS. 45 

a vapour which cooled down into a very strong acid, now 
called nitric acid. He used this to dissolve silver, and by 
mixing it with sal-ammoniac he found it would even dissolve 
gold. Sal-ammoniac was a kind of salt which was known 
to the Arabs before Geber's time. They made it by heat- 
ing the dung of camels, and the name ammoniac was given 
to it because they made it first in the desert near the temple 
of Jupiter Amnion. Geber also made sulphu ric acid by dis- 
tillinffajum. When we remember that all these experi- 
ments were made more than a thousand years ago, we must 
acknowledge that Geber deserves great honour for the dis- 
coveries which he made. 

Albategnius, 879. — We have seen that in chemistry 
the Arabs learned very little from the Greeks, but in mathe- 
matics and astronomy they found a great deal written, and 
the Arabian astronomers spent much of their time in trans- 
lating Greek works. Unfortunately they mixed up astro- 
nomy, or the study of the heavenly bodies, with astrology, a 
kind of magic art, by which they imagined they could fore- 
tell what was going to happen by studying the stars. It 
was the Arabs, however, who preserved the knowledge of 
astronomy for nearly 700 years. In 964 Al Sufi re-estimated 
the brilliancy of the stars in Ptolemy's catalogue; while A~ 
Albategnius, born a.d. 879, calculated the length of the 
year more exactly than Ptolemy had done, mak ing it 36 5 
days 5 hours 46 minutes 24 se conds, which was only two 
minutes shorter than it really is. In a.d. 1008 Ebn Junis 
drew up several astronomical tables, and in 1437 Ulug Beg 
made the second original catalogue of stars. 

Ben Musa, 900. — Of mathematicians, one of the most 
celebrated was Mohammed Ben Musa, who lived about 
a.d. 900. He is the ea rliest A rabian writer on Algeb ra, or 
the working of sums by means ot letters, although we find 



qI^ 



46 SCIENCE OF THE MIDDLE AGES. pt. ii. 

that a Greek writer, Diophantus, made use of this method 
some time in the fifth century. This name ' Algebra ' is an 
Arabian word, and the Arabs were very clever at this way 
la^J" of making calculations. Ben Musa is the firs t wri ter we 
^^L^^Xknow of who used the India n numerals i, 2, 3, 4, 5, 6, 7, 
vt^" 8, 9, o, instead of the clumsy Roman numerals I. II. III. 

IV. ; etCr If you try to do a sum with the Roman numerals 
you will see what a troublesome business it is, and what a 
great gain the Indian numerals are. The Arabs learned these 
figures j rom the Hindo os, and always used them after the 
time of Ben Musa, so that they are now generally called 
the Arabic numerals. About the year 1000, a Frenchman 
named Gerbert, Archbishop of Rheims, and afterwards Pope 
Sylvester the Second, who had been educated at the famous 
Arabian University of Cordova in Spain, introduced them 
into Europe. The word cipher, which we use for o, comes 
from an Arabic word, ciphra, meaning empty or void. 

Alhazen's discoveries in Optics, 1000.— Another 
Arabian whom we must specially mention, was an astro- 
nomer and mathematician named Alhazen, who was born at 
Bassora, in Asiatic Turkey, about a.d. iooo, but who spent 
most of his life in Spain. He made discoveries chiefly in 
optics, or the science of light and vision. He was the first 
~to""tea"ch that we see things b ecaus e ra ys of li ght from the 
■lo-ui im^ objects aro und us strike upon the retina or thin membrane 
< b~~* JL ^t of our eye, and the impr ession is carried to our brai n by a 
nerve. When the object is itself a light, like the flame of 
a candle, it gives out the rays which reach our eye ; but 
when, like a book or a chair, it is not luminous, then the 
rays of the sun or any other light-giving body are reflected 
from it to our eye and make a picture there. Alhazen also 
explained why we do not see two pictures of one object, 
although we look at it with two eyes ; he pointed out that, 





ch. vii. ALHAZEN ON REFRACTION. 47 

as the reflection of any given point of the object is formed 
on the same part of the one eye as of the other, only one 
united picture reaches the brain. This is the best explana- 
tion which has ever been given of why we only see one 
image, but even to this day we are not quite certain that it 
is satisfactory. 

Alhazen discovered another wonderful thing about light. 
If you take a straight stick and hold 
it in a slanting direction in a basin 
of water so that half of it is under 
water and look at it from above, the 
stick will appear to bend at the 
point a, where it touches the surface 
of the water, and instead of going ^f^T 

along the dotted line to b, will look 0/ J 

as if it went to the point c. This is because rays of light are [ff^f/ 
bent in a slanting or oblique direction when they pass through (rfJu^ 
substances of different density. Water is more dense than (J V 
air, and therefore the rays of light reflected from the stick 
are bent as they pass out of the water into the air on their 
way to your eye. This is called refraction , or the breaking- 
back of a ray, and the discovery of it led Alhazen to find 
the explanation of a very curious natural fact. 

He knew that the air round our globe grows dense r as it jQje***f 
gets n earer the earth, so he argued that the slanting rays 
from the sun, moon, and stars must become bent as they 
approach the earth and pass through the denser air. This, 
he said, causes us to see the sun after it has really sunk 
below our horizon at night, and before it rises in the morn- 
ing ; for the rays are gradually curved by passing through 
the denser air round our earth. Fig. 4 explains this. Sup- 
posing the sun to be at s, and a person at a, it is clear 
that any straight ray from the sun, such as s d, could not 



48 



SCIENCE OF THE MIDDLE AGES. 



PT. II, 



reach a, because part of the earth is in the way • neither 
could a ray, s c, reach the earth, because it would pass 
above it. But when the rays from s to c strike the atmo- 
sphere at b, they are bent out of their course, and are 
gradually curved more and more by the denser air till they 
are brought down to the earth at a, and so the sun becomes 
visible. v C 




Fig. 4. 
Bending of the Sun's rays by the atmosphere. 
S, Sun. s c and s d, Rays as they would travel if there were no atmosphere. 
s B a, Ray bent so that the sun becomes visible from a. 

Alhazen was also th e firs t to explain jvhy_.a convex lens, 
that is, a glass with rounded surfaces, such as our common 
magnifying glasses and burning glasses, will makejhings_ap- 
pear larger if held at a proper distance between the eye and 
anyorjject ; namely, because the two surfaces of the glass, 
becoming more and more oblique to each other as they 
approach the sides, bend the rays inwards, so that they 
come to a focus in the eye. To understand this, draw a 
line of any kind, say a little arrow, on a sheet of paper, and 
bring your eye near to it. Your arrow being so close 
would look very large if you could see it distinctly, but just 
because it is so near, your eye cannot focus or collect to- 
gether the rays coming from it so as to make a picture on 
the retina at the back of the eye ; therefore you see nothing 
but an indistinct blur. But now, keeping your eye in the 



ch. vii. ALHAZEN— MAGNIFYING GLASSES. 49 

same position, take a magnifying glass, c d, Fig. 5, and hold 
it between your eye and the arrow. If you hold it at the 
right distance you will now see the arrow distinctly, because 
the greater part of the rays have been bent or refracted by 
the rounded glass so as to come into focus on your retina. 
But now comes another curious fact. It is a law of sight, 
that when rays of light enter our eye we follow them out in 
straight lines, however much they may have been bent in 
coming to the eye. So your arrow will not appear to you 

A 




Fig. 5. 

Arrow magnified by a convex lens. 
a 5, Real arrow ; c d, Magnifying glass ; a b, Enlarged image of the arrow. 

as if it were at a b, but, following out the dotted lines, 
you will see a magnified arrow, a b, at the distance at which 
you usually see small objects distinctly. This observation 
of Alhazen's about the bending inwards or converging of 
rays through rounded glasses was the first step towards 
spectacles. 

Besides the Arabians whom I have mentioned here, there 
were many who were very celebrated, but we know very 
little of their works. Among them was Avicenna a.d. 980, 
whom you will often hear mentioned as a writer on minerals. 
But the chief thing to be remembered, besides the dis- 



5o 



SCIENCE OF THE MIDDLE AGES. 



PT. II. 



coveries of Geber and Alhazen, and the introduction of the 
Indian numerals, is that in the Dark Ages, when all Europe 
seemed to care only for wars and idle disputes, it was the 
Arabs who kept the lamp of knowledge alight and patiently- 
led the way to modern discoveries. 



SaJ&A" 1 ^ 



°r=~^LZ~~~ 




/; 



itf Jh& l^p* <*^&-*~^~^ls c *' 





^P^strf^^*-*** 



dJc^- %~"^» **~ 



ch. viii. ROGER BA COM 




feS: 



CHAPTER VIII. 

SCIENCE OF THE MIDDLE AGES (CONTINUED). 

Roger Bacon — His ' Opus Majus ' — Flavio Gioja invents the Mariner's 
Compass — Use of the Compass in discovering new Lands — Colum- 
bus — Vasco de Gama — Magellan — Invention of Printing — Leon- 
ardo da Vinci. 

We must now return to Europe, where the nations were 
struggling out of the Dark Ages ; and though there were 
many learned men in the monasteries, very few of them 
paid any attention to science: while those who did, often 
lost their time in alchemy, trying to make gold; or in 
astrology, endeavouring to foretell events by the stars. 

Roger Bacon, 1214. — In the year 12 14, however, a 
man was born in England whom every Englishman ought 
to admire and revere, because in those benighted times he 
gave up his whole life to the study of the works of 
nature, and suffered imprisonment in the cause of science. 
This was Roger Bacon, a great alchemist, who was born at 
Ilchester in Somersetshire, educated at Oxford and Paris, 
and then became a friar of the order of St. Francis. For 
this reason he is often called Friar Bacon. Bacon's great 
work, called the ' Opus Majus,' is written in such strange 
language that it is often difficult to find out how much he 
really knew and how much he only guessed at. We know, 
however, that he made many good astronomical observa- 



52 SCIENCE OF THE MIDDLE AGES. ft. IT. 

tions, and that he explained the rainbow by sayin g that the 
sun's rays are refracted or bent back by the falling drops 
of rain, as was also noticed about the same time by Vitellio, 
a Polish philosopher. 
* j j Bacon is famous as the first man in Europe jw ho made 
^ ^ <7t4 ^^ gun powder ; we do not know whether he learnt the method 
from the Arabs, but it is most likely, for he gives the same 
receipt for making it as Marcus Grsecus did — namely, salt- 
petre, charcoal, and sulphur. He also knew that there are 
different kinds of gas, or air as he calls it, and he tells us 
that one of these puts out a flame. He invented the 
schoolboy's favourite experiment of burning a candle under 
a bell-glass to prove that when the air is used up the 
candle goes out. 

Bacon see ms also j to have known the theory o f a te le- 
scope. We clo not know whether he ever made one, but 
he certainly understood how valuable it would be. This 
is what he says about it in his ' Opus Majus,' or ' Greater 
Work ' : ' We can place transparent bodies (that is, glasses) 
in such a form and position between our eyes and other 
objects that the rays shall be refracted and bent towards 
any place we please, so that we shall see the object near at 
hand, or at a distance, under any angle we please; and 
thus from an incredible distance we may read the smallest 
letter, and may number the smallest particles of sand, by 
reason of the greatness of the angle under which they 
appear.' This is at least a very fair description of the tele- 
scope and of the microscope. In the same book he says 
that one day ships will go on the water without sails, and 
carriages run on the roads without horses, and that people 
will make machines to fly in the air. This shows that he 
must have had some knowledge of many things which were 
not really discovered till more than 300 years afterwards: 



ch. viii. FLA VIO GIOJA MARINER'S COMPASS. 53 

though he does not tell us how he arrived at them. Be- 
fore we leave Roger Bacon I must warn you not to con- 
fuse him with Francis Bacon, Chancellor of England, who 
was quite a different man, and lived more than 200 years 
later. 

Flavio Gioja discovers the Mariner's Conrpass f 
1300. — About ten years after the death of Bacon, a man 
was born in a little village called Amain, near Naples, who 
made a discovery of great value. The man's name was 
Flavio Gioja, and the discovery was that of the mariner's 
compass. Long before Flavio's time people knew that there 
was a kind of stone to be found in the earth which attracted 
iron. There is an old story that this stone was first dis- 
covered by a shepherd, who, while resting, laid down his 
iron shepherd's crook by his side on a hill, and when he 
tried to lift it again it stuck to the rock. Although this 
story is probably only a legend, yet it is certain that the 
Greeks and most of the ancient nations knew that the load- 
stone attracted iron ; and a piece of loadstone is called a 
magnet, from the Greek word magnes, because it was sup- 
posed to have been first found at Magnesia, in Ionia. 

A piece of iron rubbed on a loadstone becomes itself a 
magnet, and will attract other pieces of iron. But Flavio 
Gioja discovered a new peculiarity in a piece of magnetised 
iron, which led to his making the mariner's compass. He 
found that if a needle or piece of iron which has been 
magnetised is hung by its middle from a piece of light 
string, it will always turn so that one end points to the 
north and the other to the south. He therefore took a 
piece of round card, and marking it with north, south, east, 
and west, he fastened a magnetised needle upon it pointing 
from n. to s.-; he then fastened the card on a piece of cork 
and floated it in a basin of water. Whichever way he 




54 SCIENCE OF THE MIDDLE AGES. pt. ii. 

turned the basin the needle carried the card round till the 
n. of the needle pointed to the north, and the s. to the 
south, and from the other marks on the card he could then 

tell the direction of the west, 
north-west, etc. 

It is easy to see how im- 
portant this discovery was ; for 
when a ship is at sea, far from 
land, there is nothing to guide 
_. . . „ Fig. 6. t i ie ca pt a in except the stars, 

it lavio s Compass floating on water. L x 

and they cannot always be 
seen, so that before he had a compass he was obliged to 
keep in sight of land in order to find his way. But as soon 
as he had an instrument which pointed out to him which 
way his ship was going, he could steer boldly and safely 
right across the sea. 

There has been much dispute as to who first discovered 
the compass, and some people think that the Chinese used 
it in very early times ; but learned men now agree that 
Gioja discovered it independently, and it is certain that he 
was the first to use it in a ship. Of course it would have 
been very inconvenient to have it always floating in a basin 
of water ; so the card was fitted, by means of a little cap, 
on to the top of a pin, round which it could turn easily, 
and this is the way it is still made. As the king of Naples 
of that day belonged to the royal family of France, Gioja 
marked the north point of the needle with a fleur-de-lys in 
his honour, and the mariner's compass of all nations still 
bears this mark. The territory of Principiato, where Gioja 
was born, has also a compass for its arms, in memory of 
his discovery. * 

Invention of Printing, 1455. — Before we go on to 
speak of the wonderful voyages which followed the inven- 



ch. viii. INVENTION OF PRINTING. 55 

tion of the compass, we must pause a moment to notice 
another great change which took place in Europe about 
a hundred years after the time of Bacon and Gioja. 
This was the inventi on of printing. 1 In the early part 
of the fifteenth century some people began to engrave, that 
is, to cut on wood, pictures and texts of Scripture, and then 
to rub them over with ink, and take an impression of them 
on paper. One day it occurred to a man named John 
Qutenberg, of Strasburg, that if the letters of a text could 
be made each one separate, they might be used over and 
over again. He began to try to make such letters, and 
with the help of John Faust of Mayence, and Peter SchoerTer 
of Gernsheim, both of them working mechanics like himself, 
he succeeded in making metal letters, or types as they are 
called. These men finished printing the first Bible in the 
yea r i4-5_£ . In 1 465 the fi r st prin ting-press was started in 
Italy, and another in Pa ris in 1469, while Caxton introduced 
printing into England in 1474. 

This invention was a great step towards new knowledge. 
So long as people were obliged to write out copies of every 
work, new books could only spread very slowly, and old 
books were very dear and rare ; but as soon as hundreds 
of copies could be printed off and sold in one year, the 
works of the Greeks on science were collected and published 
by clever men, and were much more read than before ; and 
what was still more important, books about new discoveries 
passed quickly from one country to another, and those who 
were studying new truths were able to learn what other 
scientific men were also doing. Thus printing was one of 
the chief steps out of the ignorance of the Dark Ages. 
CL* Voyages round the World. — The next step, as I said 

1 The art of printing appears to have been practised by the Chinese 
as early as the beginning of the eighth century. 



56 SCIENCE OF THE MIDDLE AGES. PT. IL 

just now, was made by the use of the mariner's compass. 
//The Greeks, as you will remember, knew that the earth was 
4>. a globe, but all this had been forgotten in Europe since the 
Goths and Vandals came in, and people actually went back 
to the old idea that the world was flat like a dinner-plate, 
with the heavens in an arch overhead. Nevertheless, the 
sailors, who saw ships dip down and disappear gradually as 
they sailed over the sea, could not help suspecting that it 
must be a round globe after all j and Christopher Columbus, 
a native of Genoa, was convinced he could find a way round 
to the East Indies by sailing to the west across the Atlantic. 
Full of this idea, he started on August 3, 1492, with three 
small ships and ninety men, from Palos, near Cadiz, in 
Spain, and sailed first to the Canary Islands. From there 
he sailed on for three weeks, guided by his compass, but 
without seeing any land ; the food in the ship began to run 
short, and his men became frightened and threatened to 
throw him overboard if he would not turn back; but he 
begged them to continue for three days longer, and a little 
before midnight on October 1 1 there was a cry of ' land ! 
land ! ' and next morning at sunrise they disembarked on 
one of the Bahama Islands in the New World. 

Columbus thought that he had sailed right round and 
reached the other side of Asia, but if you look at your map 
you will see he only went a quarter of that distance. He 
died in 1506, without finding out his mistake, though he 
made several other voyages. During these he made a very- 
remarkable discovery about the magnetic needle of the 
compass. It had long been known that the needle did not 
point due north, but a little to the east of the north. 
Columbus, however, found that, as he went westward, the 
needle gradually lost its eastward direction, and pointed 
due north, and then gradually went a little way to the west. 



\ 



ch. vni. VOYAGES ROUND THE WORLD. 57 

It remained like this till, on his return, he came back to 
the same place where it had changed, and then it passed 
gradually back to its first position. From this he learnt 
that, although the magnetic needle always points towards 
the north, it varies a little in different parts of the world. 
The reason of this is not even now clearly understood, and 
we must content ourselves here with knowing that it is so. 

The next grand voyage of discovery was made by Vasco^ 
de Gama, a Portuguese, who set sail July 9, 1497, to try 
whether it was possible to sail round the south of Africa. 
He succeeded, and during the voyage he could not help 
remarking the new constellations or groups of stars, never 
seen in Portugal, which appeared in the heavens. This 
proved to him that the earth must certainly be a globe, for / 
if you were to sail for ever round a flat surface, you would J) 
always have the same stars above your head. 

At last there came a third discoverer, Ferdinand Magellan 
(or Magalhaens), of Spain, who set off August 10, 15 19, 
determined to sail right round the world. He steered 
westward to South America, and discovered the Straits 
which separate Terra del Fuego from the mainland, and 
which were called after him the Straits of Magellan. Then 
he sailed northwards, across the equator again, till he came 
to the Ladrone Islands, where he was killed fighting a 
battle to help the native king. Sebastian del Cano, his 
lieutenant, then took the command of the ship, which 
arrived safely back in the port of St. Lucar, near Seville 
in Spain, on September 7, 1522. This ship, guided by 
Magellan, was the first which ever sailed quite round the 
world ; and all these voyages, proving that the earth is a 
round globe, and bringing back accounts of new stars in 
the heavens, set men thinking that there was much still to 
be learnt about the universe. 



58 SCIENCE OF THE MIDDLE AGES. ft. ii. 

Leonardo da Vinci, 1452.— We must not pass on into 
the sixteenth century without mentioning Leonardo da 
Vinci, th e great painter , who was also very remarkable for 
the number of interesting inventions which he made in 
mechanics. Leonardo was born in 1452 at Vinci, in 
Tuscany; he is so generally spoken of as a painter that 
many people do not know that he left behind him fourteen 
valuable works on Natural Philosophy. He invented 
jivater-mills and water-engine s, as well as locks to shut off 
the water, such as are now used on our canals and rivers. 
He studied the flight of bird s, and tried to make a mechani- 
cal a pparat us for flying, and, besides being one of the best 
engineers of his day, he made many curious machines, such 
as a spinn ing mac hine, a water-pu mp, and a planing- 
machine. Some of these things were only models which 
he made for his own pleasure, but they show that he, like 
Roger Bacon, was very much in advance of his age ; and 
he did good service to science by the careful experiments 
which he made, and by insisting that it was only by going 
to Nature herself that men can really advance in knowledge. 



Chief Works consulted. — Draper's 'Hist, of Intellectual Develop- 
ment ;' Baden Powell's ' Hist of Natural Philosophy,' 1834 ; Sprengel 
' Histoire dela Medecine,' 1850 ; ' Penny Cyclopaedia,' art. 'Arabians ;' 
* Encyclopaedias Metropolitana and Britannica ; ' Rodwell's ' Birth of 
Chemistry,' 1874 ; 'The Works of Geber,' Englished by R. Russell, 
1678; Whewell's ' Histoiy of the Inductive Sciences;' Priestley's 
' History of Vision,' 1772 ; Smith's ' Optics, 5 1778 ; ' Edinburgh En- 
cyclopaedia,' art. Chemistry ; Bacon's ' Opus Majus,' by Dr. Jebb, 
17333 Bacon, ' Sa Vie, ses Ouvrages, et ses Doctrines,' by M. 
Charles, 1 86 1 ; Ventura, 'Ouvrages Physico-mathematiques de Leon- 
ardo da Vinci,' 1 797 ; Draper's ' Conflict between Religion and 
Science,' 1875. 



PART III. 

RISE AND PROGRESS OF 
MODERN SCIENCE 

FROM A.D. 1500 TO THE PRESENT DAY 



Chief Scientific Men of the Sixteenth Century. 









A.D. 


Copernicus 




1473-1543. 


Paracelsus . 






1493-1541. 


Vesalius . , 






1514-1564. 


Fallopiua . 






1520-1563. 


Eustachius . 






— -1570. 


Gesner . , 






1516-1565. 


Csesalpinus 






1519-1603. 


Baptiste Porta 






1545-1615. 


Gilbert 






1 540- 1 603. 


Tycho Brahe 






1546-1601. 


Galileo 






1 564- 1 642. 


Stevinus 






— 1633. 


Van Helmont 






1577-1644. 


Giordano Bruno 






— -1600. 



CH. ix. SIXTEENTH CENT UK K. 61 



CHAPTER IX. 

SCIENCE OF THE SIXTEENTH CENTURY. 

Rise of Modem Science — Dogmatism of the Middle Ages — Copernicus 
— Copernican Theory of the Universe — Vesalius on Anatomy — Fal- 
lopius and Eustachius, Anatomists — Gesner the Naturalist — Csesal- 
pinus the Botanist — Chemistry of Paracelsus and Van Helmont. 

We have now arrived at the beginning of Modern Science, 
when the foundations were laid of that knowledge which we 
possess to-day. With the exception of some original dis- 
coveries made by the Arabs, learned men during the Dark 
Ages had spent their time almost entirely in translating and 
repeating what the Greeks had taught ; till at last they had 
come to believe that Ptolemy, Galen, and Aristotle had 
settled most of the scientific questions, and that no one had 
any right to doubt their decisions. But as Europe became 
more civilised, and people had time to devote their lives to 
quiet occupations, first one observer and then another began 
to see that many grand truths were still undiscovered, and 
that, though the Greeks had learned much about nature, yet 
their greatest men had only made the best theories they 
could from the facts they knew, and had never intended that 
their teaching should be considered as complete or final. 

And so little by little real observations and experiments 
began to take the place of mere book-learning, and as soon 
as this happened science began to advance rapidly — so 
rapidly that from this time forward we can only pick out the 



62 SIXTEENTH CENTURY. pt. hi. 

most remarkable among hundreds of men who have added 
to the general stock of knowledge. A detailed account of 
all the steps by which the different sciences progressed would 
fill many large volumes, and would only be confusing except 
to those who already know a great deal about the subject 
In this book we can only throw a rapid glance over the last 
four centuries of modern science, and try to understand such 
new discoveries as ought to be familiar to every educated 
person. It is, therefore, very important to bear in mind 
that when we come to a great man who discovers or lays 
down new laws, there have always been a number of less- 
known observers who have collected the facts and ideas from 
which he has formed his conclusions, although to mention 
all these men would only fill the pages with a string of use- 
less names. 

It is also necessary to explain why the plan is adopted 
of giving new discoveries in the order in which they occurred. 
Each separate science would no doubt have been easier to 
follow, if the account of it had been carried on without any 
break — if, for example, Astronomy had been spoken of first, 
then Optics, then Mechanics, and so on. But this arrange- 
ment would not show the gradual way in which our know- 
ledge has grown from century to century, nor how the work 
done in one science has often helped to bring out new 
truths in another. Therefore, although by following the 
order of dates we shall be forced sometimes to pass abruptly 
from one subject to another, this is, I believe, the best 
method of teaching the ' History ' of Modern Science. 

Copernican Theory of the Universe, 1473-1543.— 
It was stated (p. 32) that about a.d. 100 Ptolemy formed a 
' System of the Universe ' which supposed our little earth to 
be the centre of all the heavenly bodies ; and the sun, 
together with all the stars and planets, to move round us 



ch. ix. COPERNICAN THEORY OF THE UNIVERSE. 63 

for our use and enjoyment. This system had been held 
and taught in all the schools for nearly fourteen hundred 
years, when, in the beginning of the sixteenth century, a 
man arose who set it aside, and proposed a better explana- 
tion of the movements which we see in the heavens. 

In 1473, a f ew years before Columbus sailed for America, 
Nicol as Cope_r njLcus, the son of a small country surgeon, 
was born at Thorn, in Poland. From his earliest boyhood 
he had always a great love for science, and after taking a 
doctor's degree at Cracow, he went as Professor of Mathe- 
matics to Rome. About the year 1500 he returned to his 
own country and was made a canon of Frauenberg, in 
Prussia. Here he set himself to study the heavens from 
the window of his garret, and often all night long from the 
steeple of the cathedral. At the same time he read care- 
fully the explanations which Ptolemy and other astronomers 
had given of the movements of the sun and planets. But 
none of their theories satisfied him, for he could not make 
them agree with what he himself observed, and, moreover, 
they required so many unlikely suppositions that it seemed 
almost impossible they could be true. For example, 
according to the Ptolemaic system, the movements of 
Venus and Mercury could only be explained by supposing 
a rigid bar, or something equivalent to it, to be connected 
at one end with the earth, and at the other with the sun, 
and these planets to revolve round some point on the same 
bar. The movements of Mars, however, being much more 
irregular, could not be explained by one bar, but required 
that this bar should have a joint at some point beyond the 
sun, so as to form a second bar revolving round the first, 
and even a third joint and a third bar were necessary to 
account for the whole of his irregularities. In order to get 
rid of this cumbersome and intricate machinery, which was 



64 SIXTEENTH CENTURY. pt. lit. 

called the ' Theory of Epicycles/ Copernicus, after twenty 
years of labour, turned back to the simple explanation 
which Aristarchus had given (p. 21), and which was called 
the Pythagorean System, namely, that the sun stands still 
in the centre of our system, and that the earth and other 
planets revolve round it. 

He had made a large quadrant, that is, an instrument 
for measuring the angular height of the sun and stars, 
and with this he made an immense number of observations 
on the different positions of the sun during the year, all 
proving how naturally the movements of the different planets 
are explained by supposing the sun to stand still in the 
middle. This he wrote down in his great work called ' The 
Revolutions of the Heavenly Bodies,' in which he taught that 
the earth must be round, and must make a journey every 
year round the sun. He gave his reasons for believing that 
Ptolemy was mistaken in believing the earth to be the 
centre of the universe, and added a diagram of the orbits 
of our earth and of the planets round the sun. He then 
went on to found upon this a whole system of Astronomy, 
too complicated for us to follow here ; but he did not pub- 
lish it, because he was afraid of public opinion ; for people 
did not like to believe that our world is not the centre of 
the whole universe. At last his friends persuaded him to 
let his book be printed, and a perfect copy reached him 
only a few days before his death, which occurred in 1543, 
when he was seventy years of age. 

f This work was the foundation of modern astronomy, 
and the theory that the earth and planets move round the 
..sun has ever since been called the Copemican Theo ry ; but 
at the time it was published very few persons believed in it, 
and it was not till more than sixty years after the death of 
Copernicus that Galileo's discoveries brought it into general 
notice. 



lUtUtfi** H? ®r~ ^r 

? * . — ^ <£cu* *>u^* *?^>- ^^-^ 



* 




ch. ix. VESALIUS AND GALEN. 65 

Work of Vesalius on Anatomy, 1542. — While Co- 
pernicus was proving to himself that Ptolemy's theory of the 
heavens was not a true one, a Belgian, named Vesalius, was 
beginning to suspect that Galen, though a good physician, 
had described the structure of man's body very imperfectly, 
because he had only been allowed to dissect animals. 

Andreas Vesalius was born at Brussels in 15 14. When 
he was quite a boy he had a passionate love for anatomy, 
and, as he had some little fortune, he gave up all his time 
to this study, and often ran great risks in order to get bodies 
to dissect ; for in those days it was still considered wicked 
to cut up dead bodies. In the year 1540 he became Pro- 
fessor of Anatomy at the University of Padua, in Northern 
Italy, and two years afterwards, when he was only twenty- 
eight years of age, he published his ' Great Anatomy/ in 
which Human Anatomy , or the structure of man's body, was 
carefully studied and described • the different parts being 
illustrated by the most beautiful and accurate wood engrav- 
ings, drawn by the best Italian artists. 

In this book Vesalius pointed out that Galen, having 
learnt his anatomy from the bodies of animals, had described 
incorrectly almost all the bones which are peculiar to man. 
For example, in animals the middle part of the upper jaw, 
which holds the front and eye-teeth, is a bone separate from 
the sides of the jaw, and even in monkeys it remains sepa- 
rate while they are young ; but man is born with the upper 
jaw all joined into one solid piece. Now Galen had de- 
scribed man's upper jaw as composed of separate bones, 
and therefore it was clear that he had made his description 
from the skull of an animal. In all instances like this, and 
there are many, in which man differs from animals, Vesalius 
showed that it was necessary to ex amine the human skele- 
ton, and not to trust merely to Galen's teaching. 



56 



SIXTEENTH CENTURY. 



PT. III. 




This was a great step in science, and yet people had 
become so accustomed to follow authority blindly that 
Vesalius made many enemies by venturing to think that 
Galen could be wrong. It happened, unfortunately, that 
one day when he was dissecting the body of a Spanish 
gentleman who had just died, the bystanders thought that 
they saw the heart throb. His enemies seized upon this 
circumstance and accused him of dissecting a living man, 
and the judges of the Inquisition would have condemned 
him to death, if Charles V. of Spain, whose physician he 
had become, had not persuaded them to send him instead 
on a pilgrimage to Jerusalem. On his return from this pil- 
grimage he was shipwrecked on the island of Zante, one of 
the Ionian islands, and died of hunger when he was only 
fifty years of age. There are of course many faulty descrip- 
tions in Vesalius's work, for the study of anatomy was at 
that time only beginning ; but he made the first attempt to 
appeal to facts instead of merely repeating what others had 
taught, and by this he earned the right to be called the 
Founder of Modern Anatomy. 

There lived at the same time as Vesalius two other very 
■^celebrated anatomists, Gabriel Fallopius, of Modena, and 
Bartholomew Eustachius , of San Severino, near Naples, who 
both did a great deal to advance anatomy. Eustachius 
described the tube running between the mouth and the ear 
which is still called Eustachian tube, and made many very 
useful experiments ; but, on the other hand, he attacked 
Vesalius very bitterly for his criticism of Galen's anatomy. 
-~^ J5Lesner's Works on Animals anrl Plants — 1f> 5 U 
i£j35i=r-We now come to one of the most interesting lives 
of the sixteenth century. Many of us know very little of 
astronomy or anatomy, but any child who has gathered 
flowers in the country or looked at wild animals in the 



ch. ix. THE FIRST ZOOLOGICAL CABINET. 67 

Zoological Gardens must feel interested in Gesner, the first 
man since the time of Aristotle who wrote anything original 
about animals and plants. 

Conrad Gesner was born at Zurich in 1 5 1 6. He was 
the son of very poor parents, and, being left an orphan, was 
educated chiefly by the charity of an uncle and other friends ; 
but his love of knowledge was so great that he conquered 
all difficulties, and after taking his degree as a medical man 
in 1540, earned enough by his profession, and as Professor 
of Natural History at Zurich, to carry on his favourite studies. 
He learnt Greek, Latin, French, Italian, English, and even 
some of the Eastern languages, and read works of science in 
all these tongues ; and although he was very delicate, he 
travelled all over the Alps, Switzerland, Northern Italy, and 
France, in search of plants, and made journeys to the 
Adriatic and the Rhine in order to study marine and fresh- 
water fish. He employed a man exclusively to draw figures 
of animals and plants, and he made a zoological cabine t, 
which contained the dried parts of animals arranged m 
their proper order. This w as probably the firs t zoological 

)inet which ever existed. He also founded a botanical 



garden at Zurich, and paid the expenses of it himself. He 
took great interest in studying the medical uses of plants, 
and often hurt his health by trying the effects of different 
herbs. His friends once thought he had killed himself by 
taking a dose of a poisonous plant called ' Doronicum,' 
or ' Leopard's Bane,' but he recovered, and gave them a 
most interesting account of his own symptoms. 

Between the years 1 q =; 1 and 156^ Gesner published 
famous { Hist ory of Animals/ in five parts ; two on quadru 
peds, one on birds, one on fish, and one on serpents. In this 
book he describes every a.n jrppl then knowr^ and gives the 
countries it inhabits and the names it has been called, both 



his \ 



68 SIXTEENTH CENTURY. pt. hi. 

in ancient and modern languages. He calculates the ave- 
rage length of its life ; its growth, the number of young ones 
it will bring up, and the illnesses to which it is subject ; its 
instincts, its habits, and its use ; and to all this he adds care- 
ful drawings of the animal and its structure. Part of his 
information he gathered from books and friends, but the 
larger part he collected himself with great care, and to him 
we owe the first beginni ng of the Natural H istory of Animals 
in modern t imes . 

In Botany he ma de thej Srst. attempt at. a true-dassificj^ 
tion of plants, and pointed out that the right way to disco^_ 
ver which plants most resemble each other is to study their 
flowers and seeds. Before his time plants had been arranged 
merely according to their general appearance ; but he showed 
that this system is very false, and that, however different 
plants may look, yet if their seeds or flowers are formed 
alike, they should be classed in the same group. He did 
not live to publish his great work on plants, but left draw- 
ings of 1500 species, which were brought out after his death. 
/" Gesner also wrote a book on Mineralo gy, in which he 
' traced out the forms of the crystals of different minerals and 
drew many figures of fossil shells found in the crust of the 
earth. The same year that this book was published he died 
of the plague. When he knew that his death was certain, he 
begged to be carried into his museum, which he had loved 
so well, and died there in the arms of his wife. 

There is something very grand and loveable in the life 
of Gesner. Born a poor boy, he struggled manfully upwards 
to knowledge, and became rich only to work for science. 
Every one loved him, and he was well known as a peace- 
maker among his literary and scientific friends, and for the 
readiness with which he would lay aside his own work to 
help others. Yet, though he had to earn his own living, and 



CH. ix. THE FIRST CLASSIFICATION OF PLANTS. 69 



died before he was forty-nine, he became the first botanist 
and zoologist of his time, and left remarkably large and 
valuable works behind him. He was one of the bright 
examples of what may be done by a true desire for know- 
ledge, and a humble, honest, loving nature ; for while he 
helped others, he could never have accomplished what he 
did in zoology and botany if he had not made friends all 
over the world, who were ready to send him information 
whenever and wherever they were able. 

First Classification of Plants by Csesalpinus, 1583. 
— Nearly thirty years after Gesner's death, Dr. Andrew 
Caesalpinus, a physician and Professor of Botany at Padua, 
first tried to carry out his system of grouping plants accord- 
ing to their seeds. He began by dividing plants into trees 
and herbs, as Theophrastus had done (see p. 17). Then he 
divided the trees into two classes — 1st, those which have 
the germ at the end of the seed farthest from the stalk, as 
in the walnut, where you will find a little thing shaped like 
a tiny heart lying just at the pointed end ; 2d, those which 
have the germ at the end of the seed which is nearest the 
stalk, as in the apple. The herbs he divided into thirteen 
classes, according to the number of their seeds and the way 
in which they are arranged in the seed-vessels. Some plants, 
for example, have a single pod or seed-vessel, with a number 
of seeds inside it, as our common pea ; others, like the 
poppy, have a seed-vessel divided into a number of little 
cells, each filled with seeds. 

By grouping together all the plants which had the same 
kind of seed-vessel, Caesalpinus made thirteen classes, and 
formed a system of plants which would have been a great 
help to botanists, and would soon have led them to make 
better systems if they had followed it ; but it was not gene- 
rally adopted, and for nearly a hundred years longer many 



70 SIXTEENTH CENTURY. pt. hi. 

went on in the old way, collecting and naming plants with- 
out trying to classify them. Csesalpinus knew about 1500 
species of plants, 700 of which he had collected himself. 
He was the first to point out that the use of flowers which 
have no seed-vessels, but only stamens (or little thread-like 
stalks, tipped with yellow powder), is to drop the powder or 
pollen on flowers which have only seed-vessels and no 
stamens, and by this means to cause the seeds to grow and 
ripen. Such plants which have the stamens in one flower 
and the seed-vessel in another are now called Monoecious, 
while if the flower containing the stamens grows on a dif- 
ferent pla?it from the one containing the seed-vessel, such 
plants are called Dioecious. 

Chemistry of Paracelsus and Van Helmont, 1520- 
1600. — There is very little worthy of notice in the 
chemistry of the sixteenth century ; but we must mention 
in passing two famous men : Paracelsus, who was born in 
1493 at Einsiedel in Switzerland, and Van Helmont, born 
at Brussels in 1577. 

Paracelsus was at one time Professor of Physic and Sur- 
gery at Basle, but he gave up his professorship and travelled 
about Europe during the greater part of his life. Among 
othe r things, he pointed out that air f eeds flame , and that, 
jf you put iron into sulphuric acid a n d water, a peculiar , 
kind of air rises from it. He also succeeded in separating 
gold out of a mixture of gold and silver by using aquafortis 
or nitric acid which dissolves the silver and lets the gold fall 
to the bottom of the vessel. ' He did not, however, make 
many discoveries which are valuable now, and he taught a 
great deal that was absurd and bombastic. 

Van Helmont was also a wandering physician, but as a 
chemist he was more careful in his experiments than Para- 
celsus. He seems to have known a great many different 



CH. ix. PARACELSUS AND VAN HELMONT. 71 

gases, though he did not describe them clearly, and he 
particularly mentions the gas which rises from beer and 
other liquids which ferment. He called this Gas svfottstr* 
The chief thing to remember abo ut Van Helmont is that he 
was the first writer to use the word { gas, ? which he took 
from the German word ' geist/ meaning ' spirit.' 



Chief Works consulted. — Rees's ' Encyclopaedia,' art. ' Copernicus ; 
'Encyclopaedia Metropolitana,' art. 'Astronomy;' ' Biographie Uni- 
verselle,' art. ' Copernicus ;' Gassendi's Life of Copernicus ; ' ' Encyclo- 
paedia,' art. 'Anatomy;' Cuvier, ' Histoire des Sciences Naturelles,' 
1845; D'Orbigny, 'Diet, des Sciences Naturelles' — Introduction; 
'Encyclopaedia,' art. 'Botany;' Hoefer, 'Histoire de la Physique et 
de la Chimie,' 1850. 



72 SIXTEENTH CENTURY. ft. hi, 



CHAPTER X. 

SCIENCE OF THE SIXTEENTH CENTURY (CONTINUED). 

Battista Porta — Kircher — Dr. Gilbert — Tycho Brahe, the Danisl 
Astronomer — Rudolphine Tables — Galileo on Mechanics and Phy 
sics — Summary of the Science of the Sixteenth Century. 

Battista Porta's Discoveries about Light, 1560. — The 

next discovery in science was about Light, and it was made 
by a boy only fifteen years of age. Battista Porta was born 
in Naples in 1545. He was so eager for new knowledge, 
that, when quite a boy, he held meetings in his house for 
any of his friends to read papers about new experiments. 
These meetings were called ' The Academy of Secrets,' and 
in the year 1560, when Porta was fifteen, he published an 
account of them in a book called Magia Naturalis or 
'Natural Magic.' In the seventeenth chapter of this book 
he relates the following experiment, which he had made 
himself. 

He says he found that by going into a darkened room 
when the sun was shining brightly, and making a very small 
hole in the window-shutter, he could produce on the wall of 
the room, opposite the hole, images of things outside the 
window. These images were exactly the shape of the real 
objects, and had always their proper colours; as, for example, 
if a man was standing against a tree outside the house, the 
green leaves of the tree and the different colours of the man's 
clothes would be clearly shown on the wall. There was 



ch. x. 'CAMERA OBSCURA* AND MAGIC LANTERN. 73 

only one peculiarity about the picture, it was always upside 
down, so that the man stood on his head, or the tree with 
its trunk in the air. The smaller the hole was, the clearer 
were the outline and the colours of the image, and Porta 
found that by putting a convex lens (that is, a glass with its 
surfaces bulging in the centre, see p. 49) into the hole he 
could get a still brighter and clearer picture at a particular 
point in the room 




Fig. 7. 

Porta knew from the works of Alhazen that rays of light 
are reflected in all directions from every object, and he ex- 
plained this image on the wall, quite correctly, by saying 
that the small hole lets in only one ray from each point of 
an object outside; the other rays, and those from the sky 
and other objects, being kept out by the shutter. Thus 
these single rays fall directly on the wall without being 
mingled with others, and so make a clear picture. It is 
easy to see from Fig. 7 that the image must be upside down, 
because the rays cross in going through the hole. This 
simple discovery of Porta's is called the ' Camera Obscura? 
or ' Dark Chamber.' You may perhaps have been into one 
at the sea-side, where they build them for visitors to watch 
the coloured reflection of the passers-by. In the camera 
obscura, as it is now made, the glasses are so arranged that 
the figures are upright. 

Porta saw at once how useful this invention would be 



74 SIXTEENTH CENTURY. ft. hi. 

for making accurate drawings of objects ; for, by tracing out 
with colours on the wall the figure of the man or tree as it 
stood, he could get a small image of it with all its propor- 
tions and colours correct. But, what is still more important, 
he was led by this experiment to understand how we see 
objects, and to prove that Alhaz'en was right in saying that 
rays of light from the things around us strike upon our eye. 
For, said Porta, the little hole in the shutter with the lens 
in it is like the little hole in our eye, which also contains a 
natural convex lens ; and we see objects clearly because the 
rays pass through this small hole. He did not, however, 
know which part of our eye represents the wall on which the 
figure is thrown, nor why we see objects upright ; we shall 
see (p. 94) that Kepler discovered this many years afterwards. 

When Porta had succeeded in getting clear images of 
real things on the wall, he began to try painting artificial 
pictures on thin transparent paper and passing them across 
the hole in the shutter, and he found that the sun threw a 
very fair picture of them on the wall. In this way he pro- 
duced representations of battles and hunts, and so made a 
step towards the Magic Lantern. He seems, however, never 
to have tried it by lamplight \ this was done by Kircher, a 
German, about fifty years later. There is no doubt that 
Porta had a very good notion of how to use two magnifying 
glasses so as to make objects appear nearer and larger, but 
ibis not certain that he ever really made a telescope. 

Dr. Gilbert, the Founder of the Science of Elec- 
tricity, 1540-1603. — It was about this time, while Baptiste 
Porta was making experiments on light in Italy, that an 
Englishman named Gilbert made the first step in one of the 
most wonderful and interesting of all the sciences, namely, 
that of Electricity. So long ago as the time of the Greeks 
it was already known that amber, when rubbed, will attract 



CH. X. DISCOVERY OF ELECTRICITY, 75 

or draw towards it bits of straw and other light bodies, and 
it is from the Greek word electron — amber, that our word 
electricity is taken. 

Until the sixteenth century, however, no one had made 
piny careful experiments upon this curious fact, and it was Dr. 
Gilbert, a physician of Colchester, who first discovered that 
other bodies besides amber, will when rubbed, attract straws, 
thin shavings of metals, and other substances. You can 
easily try this for yourself by rubbing the end of a stick of 
common sealing-wax on a piece of dry flannel, and then 
holding the rubbed end near to some small pieces of light 
papers, or some feathers or bran. You will find that these 
substances will spring towards the sealing-wax and cling to 
it for a short time, being held there by the electricity which 
has been produced by rubbing the sealing-wax. 

Gilbert showed that amber, jet, diamond, crystal, sulphur, 
sealing-wax, alum, and many other substances, have this 
power of attraction when they are rubbed, and he also proved 
that the attraction was stronger when the air is dry and cold 
than when it is warm and moist. This may seem very little 
to have discovered compared to the wonderful facts which 
we now know about electricity; but it was the first step, 
and Gilbert's book on ' Magnetism ' (as he called it), which 
was published in 1600, must be remembered as the earliest 
beginning of the study of electricity. 

Tycho Brahe, Astronomer, 1546-1601. — We must 
now return to Astronomy, in which during the next eighty 
years wonderful discoveries were made by three celebrated 
men, Tycho Brahe the Dane, Galileo the Italian, and 
Kepler the German. 

Tycho Brahe was born in the year 1546, at Helsin- 
borg, a town in Sweden, which at that time belonged to the 
Danes. When he was only fourteen he was so much 



76 SIXTEENTH CENTURY. pt. in. 

astonished that the astronomers had been able to foretell 
exactly the moment when an eclipse of the sun took place 
in 1560, that he determined to learn this wonderful science, 
which could predict events. His father had intended him 
to be a lawyer, but Tycho bought a globe and books with 
his own money, and studied astronomy in secret; till at 
last his family consented to let him follow his own inclina- 
tion, and from that time he gave himself up to that science, 
planning and making the most beautiful instruments for 
taking observations in the heavens. 

At this time the theory of Copernicus had made very 
little impression, and Tycho Brahe rejected it altogether 
and made a theory of his own called the Tychonic system, 
which was, however, soon laid aside and forgotten. This, 
however, mattered very little, for the useful work which 
Tycho did was not to lay down new laws, but to collect an 
immense number of accurate facts which were invaluable to 
the astronomers who came after him. For twenty-five 
years he lived in the little island of Huen, in the Baltic, 
which the King, Frederick II. of Denmark, had given him, 
making accurate observations of the different movements of 
the planet, and determining the positions of the fixed stars, 
of which he catalogued 777. He built there a magnificent 
observatory, which he called Uranienborg, or the City of 
the Heavens, and filled it with instruments of every kind, 
which enabled him to keep a register of the different posi- 
tions of the heavenly bodies night after night. 

When Frederick II. died, Tycho was persecuted and 
driven into exile by some envious people who grudged him 
the pension he was receiving. He then went to Bohemia, 
under the protection of the Emperor Rudolph II., and here 
he drew up the valuable astronomical tables called the 
Rudolphine tables, which, as we shall afterwards see, were 



CH. x. ORIGIN OF THE PENDULUM. 77 

of immense use to Kepler. Tycho died in 1601, before 
Galileo and Kepler made their greatest discoveries. 

Galileo's Discovery of the Principle of the Pen- 
dulum, and of the Rate of Falling Bodies, 1564-1600. 

— Galileo dei Galilei was born at Pisa in 1564. His father, 
though of good family, was poor, but being himself a man 
of talent and education, he made great exertions to send 
his son to the University of Pisa, meaning to educate him 
as a doctor. Here Galileo studied medicine under the 
famous botanist Caesalpinus ; but having also begun to learn 
geometry, he became so wrapt up in this pursuit that his father 
found it was useless to check him, and therefore wisely let 
him follow his natural bent. It was while he was still at 
the University, and before he was twenty years of age, that 
Galileo made his first discovery. When watching a lamp 
one day which was swinging from the roof of the cathedral, 
he noticed that, whether it made a long or a short swing, 
it always took the same time to go from one side to another. 
To make quite sure of this he put his finger on his own 
pulse, and, comparing its throbs with each swing of the 
lamp, found that there was always the same number of beats 
to every swing. Following up this simple observation he dis- 
covered that a weight at the end of a cord will always take 
the same time to swing backwards and forwards so long as 
the cord is of the same length and the arc through which 
the weight moves is small. This was the beginning of pen- 
dulums, such as we have now to our clocks, but at first they 
were only used by physicians to count the rate at which a 
patient's pulse beats. 

In 1589 Ferdinand de' Medici, Duke of Tuscany, having 
heard of Galileo's talents, made him Lecturer on Mathematics 
at Pisa, and it was while he held this post that he made his 
next discovery, which was about falling bodies. He ob- 



78 SIXTEENTH CENTURY. pt. hi, 

served that a stone or any other body, dropped from a 
height, falls more and more quickly from the time it 
starts till it reaches the ground, and after many experi- 
ments he succeeded in calculating at what rate its falling 
increases. At the end of the first second it will be falling 
at the rate of 3 2 feet per second, at the end of two seconds 
it will be falling at the rate of 64 feet per second, at the 
end of three seconds at the rate of 96 feet per second, and 
so it will continue, falling 32 feet faster every second till it 
reaches the ground. 

Galileo explained this increase of velocity, or quickness 
of falling, in the following way : It is the weight of the stone, 
he said, which drags it down ; and when it had been once 
started downwards by its weight, it would go on moving at 
the same rate for ever, without any more dragging. But 
the weight still goes on pulling it down just as much at the 
end of the first second as it did when it started, and so the 
stone falls, first with the drag of its start, then with the 
drag of the first second added, then of the next, and the 
next all added together, until it reaches the ground. 

This was quite a true explanation, so far as it went, and 
Galileo went on to prove another fact, which sounds very 
strange at first, namely, that if you let two weights, one 
light and the other heavy, drop from the same height, they 
will both take exactly the same time in falling to the ground. 
Galileo could not make the learned men of Pisa believe 
this, because Aristotle had said that a ten-pound weight 
would fall ten times as fast as a one-pound weight; so to 
convince them he carried different weights up to the top 
of the Tower of Pisa, and let them fall before their eyes. 
Still, though they saw them reach the ground at the same 
moment, they would not believe, so obstinately were they 
determined to think with Aristotle ; and they actually an- 



CH. x. THE RATE OF FALLING BODIES. 79 

noyed Galileo so much on account of his opinions that he 
left Pisa and became a professor at Padua in 1592. 

The best way for you to convince yourself that Galileo 
was right and they were wrong will be to take some large 
soft clay balls, say five, each exactly the same weight, and 
let them drop at the same moment from the same height — 
you can see at once that they will all reach the ground 
together. Then press four of the balls one against the 
other so that they stick together. They will now be four 
times heavier than the remaining ball, and yet if you let 
them drop from the same height again, there is no reason 
why the four should fall any faster merely because they are 
stuck together than when they were separate, and so the five 
will reach the ground together as they did before. I have 
said take large balls, because if they are not tolerably heavy 
the air will interfere with their falling accurately ; indeed, 
to make the experiment very truly it ought to be made in 
a vacuum, that is, a space from which the air has been 
pumped out, for air buoys up bodies as water does, and this 
would retard the falling of a light body, especially if it had 
much surface, while it would be inappreciable in heavier 
ones. But air-pumps were not invented in Galileo's time, 
so he could not make the experiment very accurately. 

In the year 1592 Galileo established another law in 
mechanics which is of great value, namely, that any force 
which will lift a weight of two pounds up one foot will lift a 
weight of one pound up two feet, or in other words, just as 
much as you make a weight lighter, so much higher the 
same force can lift it. If you double the weight, the same 
force will only lift it half as high ; if you treble the weight, 
it will only lift it one-third as high, and so on. This law is 
of immense value in determining the balance of machines, 
but we cannot examine it further here. At about the same 



8o SIXTEENTH CENTURY. pt. hi. 

time that Galileo was discovering these laws of motion, a 
famous engineer, named Stevinus, of Bruges, published a 
little book, in which he made known some very important 
laws about the rest and motion of bodies, which formed the 
foundation of the modern science of statics, or the stud}' of 
bodies at rest. 

G-alileo's Observations on Musical Notes. — Galileo 
appears also to have made some curious observations on 
the subject of sound, and it was he who discovered that a 
musical note is produced by a number of shocks following 
rapidly and regularly one after the other, and that the more 
quickly one shock succeeds the other, the higher the note 
will be. He relates that one day, when he was scraping a 
copper plate with an iron chisel to rub out some spots, he 
heard a whistling noise, and found on looking, that the plate 
was covered with fine streaks at regular intervals, and that 
it was the production of these streaks which gave rise to the 
musical sound. As he moved his hand more quickly the 
note became more shrill, and the streaks closer together. 
Galileo knew that the sound was caused by vibrations of 
the -particles of the air set in motion by the quivering of 
the metal, and he stated quite correctly that the reason he 
heard a higher note when the movement was more rapid, 
was, that a greater number of these vibrations struck on the 
drum of his ear in a certain space of time, thus causing it 
to vibrate more rapidly. 

Summary of the Science of the Sixteenth Cen- 
tury. — And now we must pause for a moment in the his- 
tory of Galileo, for his astronomical discoveries belong to 
the next century, and before entering upon them we must 
reckon up the advances which had been made in science 
during the past hundred years. 

I think you will agree with me that at least one grand 



CH. x. CONCLUDING REMARKS. 81 

step had been made when men learned to examine for them- 
selves, and were no longer content merely to repeat like 
parrots what the Greeks had handed down to them. Coper- 
nicus had shown in astronomy, Vesalius in anatomy, and 
Galileo in mechanics, that it was no longer enough to quote 
passages from Ptolemy, Galen, and Aristotle ; but men 
must take the trouble to examine the works of nature for 
themselves, if they wished really to understand the laws of 
the Great Creator. 

This, in itself, was a great advance; but beyond this 
Copernicus, by his new system, had opened the way for 
grand astronomical discoveries, which you will see followed 
quickly in the next century, and Tycho, by his long and 
patient observations, had stored up facts for the use of those 
who came after him. In the same way Vesaliu s in anatomy, 
and Gesner and Ca esalpinu s in natural history, had laid a J>. & 
foundation for the regular study of living beings, and had 
roughly sketched out a plan of classification. In the subject 
of light, Porta had invented the camera obscura, and ex- 
plained the principle upon which it acts ; and in doing this 
had made important discoveries about the action of light 
upon our eye, and the use of lenses, or convex and con- 
cave glasses, in magnifying objects. Lastly, Galileo had 
discovered the principle of the pendulum and the rate of 
falling bodies, and was now on the brink of the discovery 
of the telescope and all the wonders which it has revealed. 

Meanwhile the sixteenth century closed with one very 
sad event, which must be mentioned here. Giordano 
Bruno, a Dominican friar, who was born about the year 
1550, at Nola in Italy, was one of the first people who 
openly taught that the Copernican system was true. He 
ought to be peculiarly interesting to us, because he was the 
first person to teach in England that the earth moves round 



82 SIXTEENTH CENTURY. pt. hi. 

the sun. But poor Bruno was a very plain outspoken man, 
and his bold language brought him to a sad but noble 
death. When people said he should not spread the Coper- 
nican system because it was contrary to the Bible, he 
answered boldly that the Bible was meant to teach men 
how to love God and live rightly, and not to settle questions 
of science. Most people now would say that Bruno was 
right, but the judges of the Inquisition did not think so, 
and were so alarmed at his opinions that they condemned 
him to death. In the year 1600, just as the century closed, 
Bruno was burnt at the stake in Rome as an atheist, partly 
because he insisted on repeating that the earth is not the 
centre of the universe, and that there may be other in- 
habited worlds besides ours. 



Chief Works consulted. — Whewell's ' Inductive Sciences ;' Brewster's 
'Optics;' Brewster's 'Martyrs of Science,' 1874; Encyclopaedia 
Britannica,' art. 'Astronomy;' Drinkwater's 'Life oj Galileo;' 
Rossiter's 'Mechanics,' 1873; Cuvier, 'Histoire des Sciences Natu- 
relles ;' Baden Powell's * Natural Philosophy. 5 



SCIENCE OF THE 
SEVENTEENTH CENTURY 



Chief Men of Science in the Seventeenth Century. 



_Galileo 
Kepler 
Gassendi 
Horrocks 
Newton 
Halley_ 
Flamsteed 

Francis Bacon 
Descartes 



■£ 



Snellius 
Drebbel 
Torricelli 
Guericke 
P ascal 
Boyle 
Hoo£e 
-Huyghens 
rRoemer 

Mayow 
Beecher 
Stahl 

fSteno 
Iscilla 

Woodward 

Harvey 

Asellius , 
Riidbeck 
3£alp,ighi 
Leeuweniuaeck 

GjEilt- 

Rajr. 

Willughby 



I 



A.D. 
I 564- I 642. 
I57I-I630. 
I592-I65S. 
I6I9-I64I. 
I642-I727. 
I656-I742. 
I646-I7I9. 

I56I-I626. 
I596-I65O. 

I59I-I626. 
1572-1634. 
I608-I647. 
I602-I686. 
I623-I662. 
I626-I69I. 
1635-1702. 
I629-I695. 
I644-I7IO. 

I645-I679. 
I625-I682. 

1 660- 1 7 34. 

1638-1687. 
1 639- 1 700. 
1661-1727. 

1578-1657. 
1581-1626. 
1630-1702. 
1 628- 1 694. 
1632-1723. 
1628-1711. 
1628-1705. 
1635-1672. 



CO. xi. GALILEO. 85 



CHAPTER XI 

SCIENCE OF THE SEVENTEENTH CENTURY. 

Astronomical Discoveries of Galileo — The Inquisition force him to 
deny the Movement of the Earth — Blindness and Death. , 

Astronomical Discoveries of Galileo, 1609-1642. — 

The seventeenth century was not many years old when 
Galileo startled the world with discoveries such as had 
never been heard of before. He relates that when quite a 
young man he was so struck with an account given by some 
of his companions of a lecture on the Copernican theory, 
that he determined to study it, and he soon became con- 
vinced of its truth. Nevertheless, he saw how difficult it 
would be to prove that the earth moves round the sun, and 
not the sun round the earth. 

When he went to Padua he gave a great deal of time to 
the study of astronomy, and had already made some 
remarkable observations, when one day, in the year 1609, 
being in Venice, he heard that a Dutch spectacle-maker had 
invented an instrument which made distant things appear 
close at hand. 

This discovery, which Bacon and Porta had foreseen, 
was made at last almost by accident in Holland, by two 
spectacle-makers, Z acharias Tansen an d Henry Lippershey. 
It is related that Jansen's children, when playing one day 
with two powerful magnifying glasses, happened to place 



86 SEVENTEENTH CENTURY. ft. in. 

them one behind the other in such a position that the 
weathercock of a church opposite the house seemed to them 
nearer and larger than usual, and their father, when he saw 
this, fixed the glasses on a board and gave them as a 
curiosity to Prince Maurice of Nassau. Whether this story- 
be true or not, it is certain that in the year 1609, both 
Jansen and Lippershey made these rough telescopes as toys, 
though they did not know how useful they might be. But 
when Galileo heard of it he saw what valuable help it might 
afford in studying the heavens ; and he set to work immedi- 
ately, and soon succeeded in making a useful instrument. 

A diagram of Galileo's telescope is given in Fig. 8, It 
was made on the same principle as opera-glasses are now, 
with one convex lens a b, which makes the rays from the 
object bend inwards or converge, and one concave lens c d, 
which makes them bend outwards or diverge before they 
come to a focus. In Fig. 8 one complete cone of rays is 
drawn coming from the point m, and the outline of another 
cone from the point n ; there are really similar cones coming 
from all points along the arrow, but it is impossible to give 
these in a diagram. Each set of rays, as they fall on the 
lens a b, are made to converge, so that they would end in a 
point or focus, if they were not caught by the lens c d. 
But this lens having its surfaces curved inwards makes the 
rays bend outwards or diverge again, so that the end of the 
cone m reaches the eye in parallel lines at tri tri and the 
cone n at ri ri. From the eye, as you will remember 
(see p. 49), we follow them out in straight lines, and see 
the image at the angle u n, so that it appears greatly 
magnified. If you look at any object through one tube of 
an opera-glass, and keep the other eye open so as to see the 
object at its natural distance, you can cover the real image 
with the magnified one, and thus see the magnifying power 



CH. XI. 



GALILEOS TELESCOPE. 



$7 



of your glass. But when you do not compare them in this 
way you do not realise how much the object is enlarged, 
because it appears to come nearer, so as to be at some 
point between m n and o, and consequently to be less 
magnified. I must warn you that both in this diagram and 

M 




Fig. 8. 
Galileo's Telescope. 
A b, Convex lens ; c d, concave lens next the eye ; m n, real arrow ; M n, apparent 
size of arrow ; m' m' and ri ri, end of the cones of rays m and n as they reach 
the eye ; M o N, angle at which the magnified arrow is seen. 

the one at p. 95 the proportions are very much distorted, 
because a star or even a house would be an immense dis- 
tance off as compared with the length of a telescope, where- 
as, in the drawing, the arrow must be placed as near to the 
lenses as they are to each other. 

Secondary Light of the Moon. — Galileo's first tele- 
scope only magnified three times, that is, made an object 
three times larger ; but he made a second which magnified 
eight times, and then he turned it to the moon and began 
to examine the surface of that satellite. He saw the moun- 
tains of the moon, and the deep hollows buried in darkness, 
and the wide plains which he mistook for oceans. Then he 
noticed that curious light called the secondary lights which 



^ 



88 SE VENTEENTH CENTUR Y. pt. hi. 

may be seen on the dark part of the moon when only one 
quarter of it is bright and shining. Galileo discovered that 
this curious light is a reflection from the earth ; for you must 
know that we reflect the sun's light back to the moon just 
in the same way as the moon does back to us, and at the 
time when we see a new moon, the man in the moon (if 
there were such a person) would see a large full earth, and 
could wander about at night by earth-light as we do by moon- 
light. Look up at the new moon just about dusk in the 
evening, and if it is a clear night you will most likely be 
able to see a faint outline of the dark side of the moon, 
which is caused by our earth-light shining upon it 

Jupiter's Moons. — When Galileo had studied the moon 
and gazed with intense delight on the myriads of tiny stars 
in the Milky Way, he next turned his telescope to the planet 
Jupiter. To his great surprise he saw three small shining 
bodies like stars close to Jupiter, which were quite invisible 
to the naked eye. Two of them were on the east side of 
the planet and the other on the west. He waited eagerly 
for the second night, to see if Jupiter would move away from 
these stars, but he found them still together, only the two 
stars which had been on the east side had now moved round 
to the west, and they were nearer to each other than they 
had been before. He was quite puzzled as to how this could 
have happened, and watched and watched for many nights 
whenever the clouds would allow him ; and at last, on the 
fourth night after he had first seen them, he came to the 
conclusion that all three stars were moving round and round 
Jupiter, as the moon goes round our earth. A few nights 
later he found that there was a fourth star which went round 
with them ; and so Galileo dis cove red Jupiter's four moons 
in th e year 1610. 

This was the first fact in favour of the-Gope*niean theory 



en. xi. ASTRONOMICAL DISCOVERIES. 89 

which ordinary people could understand. The planets had 

till now been looked upon simply as lights in the sky moving 

round the earth ; but now it could not be doubted that 

Jupiter at least was something more than this, for he had a 

system like our own, with four moons, to give him light by 

night, instead of one. Many people were terribly alarmed 

at the fact that our little earth should not be the central 

body in the heavens, because they had hitherto believed 

that the sun, moon, and stars had all been created for our 

use only, and this could scarcely be if our world was only 

one of many bodies moving round the sun. Some astro-lj ^° * /1/ *' 

nomers would not believe that Galileo had really seenll^*^/* 

Jupiter's moons; one was even so foolish as to refuse toll fjf. 

look through the telescope, for fear he should see them. * ,° 

Phases of Venus. — Galileo, however, now felt sure /fa^^f 
that his new instrument would help him to read wonderful ft ^Cj 
truths in the beautiful universe of God, and he threw his 
whole heart and soul into this grand study. It was not long 
before he discovered another proof that the planets move 
round the sun and not round the earth. When he first saw 
the planet Venus through the telescope she was round, but 
happening to look at her one day, when she was almost be- 
tween the earth and the sun, he saw her in the form of a 
crescent like a new moon. Struck by this, he continued to 
observe her night after night till she had made the whole 
journey round the sun, and he proved to himself that she 
went through the same changes as our moon, from a crescent 
shape to a full round face. This was just what she would 
be expected to do if she and we both travelled round the 
sun, whereas if she travelled round some fixed point between 
the earth and the sun, as was supposed by the Ptolemaic 
system, she could not exhibit these phases. Thus for th e 
second time (^a1i|e<"> prnvprl that the Copernican theory was 
the true one. 



\ 



90 SEVENTEENTH CENTURY. ft. hi. 

He next turned his attention to Saturn, and before the 

end of the year he had made out that this planet was not 

single, but had something on each side of it which he thought 

were two small stars. This was Saturn's ring, but Galileo's 

telescope was not powerful enough for him to see it clearly. 

I In the year 1659 another famous astronomer, named 

/ Huyghens, saw the ring through a much better telescope, 

J and d escribed it (see Chapter XXI.) 

Sun-Spots. — Galileo had now a great wish to go to 
Rome, so that he might show the new wonders he had dis- 
covered to the learned men who lived in that city. He 
/ accordingly carried his telescope there in 161 1, and set it 
\ up in the Quirinal Garden. It was there that he first noticed 
the dark s pots on the face of the su n, and observed that they 
were not always of the same shape, but that two or three 
would sometimes run into one, or that one would divide it- 
self into three or four. These spots, which even now can 
only partly be explained by astronomers, were observed by 
/several other men, especially by an English astronomer 
\named Harriot, about the same time as by Galileo. But 
Galileo made a special use of his discovery, for he pointed 
out that the spots move round regularly in about twenty- 
eight days, disappearing on one side of the sun and re- 
< appearing after some time on the other. This proved that 
the ,§un turns round u pon its ow n axi s in twenty-eight days._ 
Galileo before the Inquisition. — And now we come 
to the sad part of Galileo's history. He was" well- received in 
Rome, and the Pope even gave him a pension of a hundred 
crowns ; but the judges of the Inquisition, who had caused 
Bruno to be burnt alive, became uneasy that Galileo should 
teach so many new things, and especially that he should 
prove that our earth was not the centre of everything, but a 
mere speck among the numberless stars and planets in the 



ch. xi. GALILEO IN ROME, 91 

heavens. They therefore sent for Galileo, in the year 16 16, 
and threatened to punish him unless he would promise to 
hold his tongue abtfut this new theory. Galileo, however, 
would not be silent ; surrounded by his little circle of admir- 
ing pupils, he could not refrain from spreading wherever he 
went the grand facts he had discovered and the truths they 
taught. He was impatient that the world should not see as 
clearly as he did how glorious the universe is when rightly 
understood, and he often spoke and wrote sharply and sar- 
castically of those who would not listen to the truth. 

At last, in 1632, he wrote a book called 'The System 
of the ^World of Galileo Galile i.' in which he clearly proved 
the truth of the Copernican theory, and alluded very angrily 
to the attempt which the Inquisition had made to force him 
to be silent. This book convinced many people, but at the 
same time it roused the anger of the judges of the Inquisition. 
They summoned Galileo (then an old man seventy years of 
age) to appear again before them ; and this time they made 
him kneel, clothed in the sackcloth of a penitent, and swear 
with his hands upon the Gospels that * it was not true that 
the earth moved round the sun, and that he would never 
again in words or writing spread this damnable heresy.' It 
is very sad to think that Galileo should thus swear to what 
he knew was a lie ; but it is still more sad that men holding 
their power in the name of God should force him to choose 
between telling a lie or being put to torture or to death as 
Giordano Bruno had been. When Galileo rose from his 
knees it is said that he stamped his foot and whispered to 
a friend : * E pur si muove ' (' Nevertheless it does move'). 

After a time he was allowed to go back to his own 
home, but never again to leave it without the Pope's per- 
mission. He went on with his studies, and made many 
useful observations ; but in the year 1636 his sight began to 
6 



> 



92 SEVENTEENTH CENTURY. pt. hi. 

fail, and he soon became totally blind. At this time he 
wrote to an acquaintance these touching words : ' Alas ! 
your dear friend and servant has become totally and irrepar- 
ably blind. These heavens, this earth, this universe, which 
by wonderful observation I had enlarged a thousand times 
beyond the belief of past ages, are henceforth shrunk into 
the narrow space I myself occupy. So it pleases God, 
it shall therefore please me also.' He died January 28, 
1642, in his seventy-eighth year; having accomplished his 
work. In spite of all opposition his discoveries had firmly 
established the truth of the Copernican system of the 
universe. 

Chief Works consulted. — Brewster's 'Martyrs of Science;' Drink- 
water's ' Life of Galileo ; ' Herschel's ' Astronomy ; ' Whewell's ' Induc- 
tive Sciences ; ' c Encyclopaedia Britannica,' art. ' Astronomy ;' Baden 
Powell's ' Hist, of Natural Philosophy ; ' Ganot's ■ Physics,' edited by 
Atkinson. 



ch. xil. THE RUD0LPH1NE TABLES. 93 



CHAPTER XIL 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Kepler the German Astronomer — His discoveries in Optics — His three 
laws — Comparison of the labours of Tycho, Galileo, and Kepler. 

Kepler, 1571-1630. — While Galileo was occupied in 
discovering unknown worlds with his telescope, another 
famous astronomer, named Johannes Kepler, was working 
out three grand laws about the movements of the planets. 
John Kepler was born in 157 1. His parents, though noble, 
were poor, and always in difficulties, but in spite of all 
obstacles he managed to educate himself, and even to take 
his degree at tKe~~ Unive rsity~~of Tu bingen. In 1594 he 
was made Professor of Astronomy at Gratz, in Styria, and 
while there he began his attempts to discover the number, 
size, and orbits of the planets, but at first with no success. 
In 1597, when the Catholics at Gratz rose against the 
Protestants, Kepler, being a Protestant, was forced to leave 
the city, and would have been in great difficulties if his 
friend Tycho Brahe had not invited him to come to Prague 
as his assistant in the observatory. Here Kepler worked 
with Tycho at his astronomical tables, called the 'Rudolphine 
Tables,' in honour of the Emperor Rudolph; and when 
Tycho died, in 1 601, he succeeded him as principal mathe- 
matician to the Emperor. 



94 SEVEXTEEXTH CEXTURY. pt. hi. 

Kepler on Optics, 1604. — Although Kepler is chiefly 
known as an astronomer, his first work, published in 1604, 
was on Optics, and in it he points out most beautifully the 
true use of the different parts of the eye. He was much 
struck with Porta' s idea that the eye is like a camera obscura, 
and he proved that the rays of light, after passing through 
the lens of the eye, form a real picture upside down on the 
fine network of nerves called the retina, at the back of the 
eye, and are then conveyed by the optic nerve to the brain 
He also pointed out that the reason why we do not see 
things upside down is that since our mind follows out each 
ray in a straight line, the ray appears to cross back again on 
the lens of the eye, and we see them as if they had never 
been inverted. This is, however, a question still undecided 
by physiologists. 

Kepler invented a much more powerful telescope than 
the one which Galileo had made. You will see by turning 
back to p. 87 that the fault of Galileo's telescope was that 
it made the rays diverge or bend outwards, just as they 
reached the eye, and in this way many of them passed out- 
side and were lost. Kepler avoided this by using two convex 
lenses. In his telescope (see Fig. 9), the rays from the 
object m n, after converging on the lens a b comes to a 
focus at m' n' where they make a real image of the arrow 
upside down. If you could put a piece of thin transparent 
paper at the point m ri in a telescope, you would see an in- 
verted picture of the object upon it. The rays from this 
image falling on the lens c d, are again bent inwards, as by 
the ordinary magnifying glass (see p. 49), and thus by follow- 
ing them out in straight lines the eye sees a magnified arrow 
/ upside down at some point between c d and M n. Kepler's 
Z telescope is called the ' Astronomical telescope.' It has a 
much larger ' field of view ' than Galileo's \ that is, it enables 



CH. XII. 



KEPLER'S 'THREE LAWS' 



C5 



you to see over a larger space at one time ; but, on the other 
hand, it turns everything upside down. In making astrono- 
mical observations it is not of much importance which part 
of a star is uppermost ; but for terrestrial telescopes another 
lens has to be put in to bring the images back to their right 
positions, and since Kepler's time many other improvements 
have been made. 




Fig. g. 

Kepler's Telescope. 1 

A B, Object-glass ; c d, eye-piece ; m n, real arrow ; m' n' , picture of the arrow 

formed at the focus of the rays ; M n, magnified arrow. 

Kepler's first Law, 1609. — After Tycho Brahe's death 
Kepler went on working at the ' Rudolphine Tables,' and 
this led him to consider again the movements of the planets, 
and to try and find a theory to explain the path or orbit of 
the planet Mars. Mars is the planet which stands fourth 
from the sun ;• Mercury is nearest to the sun, then comes 
2- Venus, then our ^arth, and then outside our earth is Mars. 
Tycho had noted in his tables the places at which the planet 
had been seen at certain periods ; and from these observa- 



1 This figure and also Fig. 
R. Wallace. 



were kindly drawn for me by Mr. A. 



96 SEVENTEENTH CENTURY. pt. hi. 

tions Kepler calculated where it ought to arrive at other 
fixed times if it moved in a circle, as the earlier astronomers 
had supposed. But he found that it did not arrive there 
as computed, and he was so sure that Tycho's observations 
were exact that he said boldly, 'All the theories must be 
wrong if they do not agree with what Tycho saw.' So he 
puzzled on, trying one explanation after another, until at 
last he discovered three remarkable laws, by which the 
movements not only of Mars, but of all the other planets, 
are explained. 

The first of these laws is that planets move round the 
sun in ellipses or ovals t and not in circles. You know that 
to draw a circle you put one leg of the compasses into a 
spot and draw the other leg round it, and the middle spot 
is called the centre or focus. But to draw an ellipse you 
must have two focuses or foci. To understand this, stick 
two pins a little distance apart in a piece of paper, and 
fasten a string to them by its two ends. Place a pencil 
upright in the string, so as to keep it tightly stretched, and 
draw the pencil round first on one side then on the other. 
You will then have an ellipse, and the two pin-holes will be 
the two foci. TDraw the sun in one of the foci and a round 
globe on some part of the ellipse, and you will have a figure 
of the path of our earth or any of the planets round the sun. 
You will find that the farther you put the pins apart the 
/ flatter the ellipse will be. The path or orbit of the planet 
L^ M^roiry is much more elliptical than the orbit of the^Earth. 
Another difference in the orbits of the planets is that they 
do not all lie in the same direction, though they all have the 
sun as one of their foci. For instance, in Fig. i o the orbit 
of the planet a has the sun for one focus and the dot c for 
the other, while the orbit of the planet b has the sun for one 
focus and the dot d for the other, and this makes the two 



KEPLER'S THREE LAWS.' 



97 




orbits lie in a different direction. Kepler's first law, then, was / < 
that planets move in ellipses . 
Kepler's Second Law, 
1609. — His second law was 
about the rate at which pla- 
nets move. He found from 
Tycho's tables that they all 
moved more quickly when 
they were near the sun 
than when they were far 
from it, and after an im- 
mense number of calculations he found the following 
rule. If you could draw a line from the sun to any planet 
on the first day of each month of the year, you would en- 
close a number of spaces, such as a, b, c, d, etc., in Fig. n, 
and each of these spaces would be the same size although not 

the same shape. For instance 
the planet, when travelling from 
i to 2 near the sun, would go 
very quickly and pass over a 
number of miles, while when 
travelling from 6 to 7 it would 
go slowly and pass over com- 
paratively few miles. And yet 
the space f will be exactly the 
same size as the space a, only 
it will be long and thin instead 
of short and broad. Kepler's second law, therefore, was that 
a line (radius vector ) drawn f rom the centre o f tli e sun t o_ a ._ St£»< 
planet sweeps over equal areas in equal times.. 

Not many months after Kepler published these two laws, 
he heard of Galileo's discoveries with his telescope — that 
Jupiter had four satellites, and that Venus had phases like 




98 SE VENTEENTH CENTUR Y. pt. hi. 

our moon, which proved that she moved round the sun. You 
may imagine how delighted he was to find the Copernican 
theory made so much more certain, and to see that the 
telescope was opening the way for so many new discoveries. 
' Such a fit of wonder,' he said, ' seized me at this report, 
and I was thrown into such agitation, that between the joy 
of the friend who told me, my imagination, and the laughter 
of both, confounded as we were by such a novelty, we were 
hardly capable, he of speaking or I of listening.' 

For many years after this Kepler was beset with troubles. 
The Emperor, being at war with his brother Matthias, had 
no money to spare for salaries. Kepler was thus harassed 
by poverty ; his favourite son died of the small-pox, which 
the troops had brought into the city, and his wife died of 
grief not long afterwards. It was not till the year 1618, 
after he had re-married and had been rescued from his 
poverty by the new Emperor Matthias, that the unfortunate 
astronomer had energy and leisure to turn again to his 
favourite planets. 

Kepler's Third Law, 1618. — It was in that year that 
he worked out with immense labour his third and most 
famous law — by which he showed how much longer the 
planets were going round the sun, according as they were 
farther off from it This is difficult to understand, but we 
must try to form some idea of it. He did not know in 
figures how far each planet was from the sun, but he knew 
the proportion of their distances, as for example, that Mars 
Js 4 time s and Ju piter 13^ times farther off from the sun 
than Mercury, and he also knew how long each was in going 
round the sun, and from these two facts he worked the 
following rule. 

If you take any two planets and cube their distance s from 
the sun and then square the time each takes in going round 



CH. xil. TYCHO BRAHE, GALILEO, & KEPLER. 99 

the sun, the two squares of the time will bear the same pro- 
portion to each other as do the two cubes of the distance. 
For instance, Mars is 4 times as far from the sun as Mer- 
,cury, and therefore it is 8 times as long going round it, 
because the cube of 4 (or 4 x 4 x 4) is 64, and the square 
of 8 (or 8 x 8) is also 64. Thus the cube of Mercury's 
distance as compared with that of Mars is 1 to 64, and the 
square of their periodic times of going round is also as 1 to 
64. This law holds equally true of all the planets, and is 
expressed in scientific language thus : ' The squares of the 
periodic times of the planets are proportional to the cubes of 
their distances? 

These three laws of Kepler were very great discoveries ; 
especially the last one, which cost him years of labour and 
calculation. He was so astonished and delighted when he 
had proved it, that he told a friend he thought at first it 
must be only a happy dream that he should have succeeded 
at last after so many failures. 

After this Kepler wrote and published many books, but 
he made no more important discoveries. The Rudolphine 
Tables were at last published in 1628, and Kepler received 
a gold chain from the Grand Duke of Tuscany for his ser- 
vices to Astronomy ; but still he could not obtain the pay- 
ment of his salary, and money difficulties pressed upon him. 
His anxiety threw him into a violent fever, and he died in 
1630 at sixty years of age. 

Work done in Science by Tycho Brahe, Galileo, 
and Kepler. — It will be instructive to notice here how 
very different these three astronomers, Tycho, Galileo, and 
Kepler were, and yet how they each did their own part to 
add to our knowledge. Tychcrwas _a man who collecte d 
facts : his work was dry, and his tables were a mass of figures, 
such as most people would think very uninteresting ; yet if 



3. 



ioo SEVENTEENTH CENTURY. pt. m. 

Tycho had not spent his life in this dry conscientious work, 

Kepler could never have d iscovered his laws. Galileo was 

a warm-hea rted enthusias tic oTiserver ; he lov ed the bea uty 

of the heavens, and knew how to make others love it too ; 

every observation he made he told in po pular lan guage to 

the world, and taught people the truth of the Copernican 

theory by showing them plainly how they could prove it for 

themselves, if they chose to look at the heavens. Kepler 

Ifaras quite different from either Tycho or Galileo; he was a 

//mathematician, and worked everything out in his own brain 

jj by accurate methods. He took Tycho's observations, which 

he knew were true, and turned them this way and that way, 

working out now one calculation, now another, and always 

throwing them aside if they were not exactly true. He spen t 

>^ years o yer his atte mpts, but it was worth wh ile, for he 

XT * arrived at three true laws, which will r emain for ev er. There 

was only one point he had not reached ; he knew that his 

laws^exe true, but h e did not know w/iv they were true. 

This was left f or N ewton to demonstrate nearly fifty years 

afterwards. 



Chief Works consulted. — Brewster's 'Martyrs of Science;' HerschePs 
'Astronomy;' Denison's 'Astronomy without Mathematics;' Airy's 

* Popular Astronomy ;' Drink water's ' Life of Kepler ;' Baden Powell's 

* History of Natural Philosophy.' 



ch. xiii. FRANCIS BACON. 'NOVUM ORGANUM.' 101 



CHAPTER XIII. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Francis Bacon, his ' Novum Organum' — Descartes — Willebrord Snellius 
discovers the Law of Refraction. 

Bacon's Influence upon Science. — Although this book 
is a history of scientific discovery and not of philosophy, 
yet we must now mention in passing two philosophers who 
lived about this time, and whose writings had great influence 
upon science. These were Francis Bacon in En-gland, and 
Rene Descartes in France. 

Francis Bacon, commonly known as Lord Bacon, was 
born in London in 1561, and died Jn 1626. He was made 
Lord Chancellor of England in 1 6 1 8, in the reign of James 
I., with the title of Lord Verulam and afterwards Viscount 
St. Alban's, and was a great political character. Bacon 
devoted much of his time to science, and, like his namesake 
Roger Bacon in the fifteenth century, he seems to have fore- 
seen many of the discoveries which were afterwards made. 
But his most useful work was a book called the ' Novum 
Organum,' or 'New Method,' published in 1620, in which 
he sketched out very fully how science ought to be studied. 
He insisted that no knowled ge can be rea l but that which 
is founded on experie nce, and that the only true wavjo_ 
cultivate sc ience is to be quite certain of each step before 
going on farther, nor to be satisfied with any general law 



// 



102 SEVENTEENTH CENTURY. pt. hi. 

until you have ex hausted all the facts which it is supposed 
to explain. 

For example, if you require to understand what heat is, 
and how it acts, you must not be satisfied, he says, by merely 
making a few experiments on the heat of the sun and that 
of fire, and trying from these to lay down some general rule 
of how heat works. ' No, you must examine it in the sun's 
rays both when they fall direct and when they are reflected ; 
in fiery meteors, in lightning, in volcanoes, and in all kinds 
of flame ; in heated solids, in hot springs, in boiling liquids, 
in steam and vapours, in bodies which retain heat, such as 
wool and fur ; in bodies which you have held near the fire, 
and in bodies heated by rubbing \ in sparks produced by 
friction, as at the axles of wheels ; in the heating of damp 
grass, as in haystacks ; in chemical changes, as when iron 
is dissolved by acids ; in animals ; in the effects of spirits of 
wine ; in aromatics, as for example pepper, when you place 
it on your tongue. In fact, you must study every property 
of heat down to the action of very cold water, which makes 
your flesh glow when poured upon it When you have 
made a list,' says Bacon, ' of all the conditions under which 
heat appears, or is modified, of the causes which produce 
it, and of the effects which it brings about, then you may 
begin to speak of its nature and its laws, and may perhaps 
have some clear and distinct ideas about it' 

You will see at once that this method of Bacon's had 
been followed already to a great extent by Copernicus, Tycho 
Brahe, Galileo, and Kepler ; but Bacon was the first to insist 
upon it as the only rule to follow, and in doing this he ren- 
dered a great service to science. 

Descartes' Condemnation of Ignorant Assertion. 
- — Rene Descartes, by his philosophy, assisted science in 
another way. He was a Frenchman, born in Touraine in 



ch. xm. WRITINGS OF DESCARTES. 103 

1596, and he became one of the most famous philosophers 
of France. He wrote a great deal on science, especially 
on mathematics and geometry, and also on the nature of 
man ; but the point which we * have to notice here was his 
belief that to arrive at the real trut h wa s the onl y thing 
worth living for . 

You will remember how the men of science of the six- ; 
teenth century had thought it a sufficient answer to Vesalius 
or to Galileo to say that Galen or Aristotle had decided 
questions of anatomy and physics ages ago ; and how the 
judges of the Inquisition thought they had crushed the 
Copernican theory when they made Galileo recant. Autho- 
rity was the idol to which these people bowed down, and 
they considered it rank heresy to doubt anything which had 
been taught by their forefathers. But Descartes said, * It 
is not true to say we know a thing simply because it has 
been told us. It is a d uty to obey authority , to submit to 
the laws and religion of our country and parents, and in 
matters where we are not able to judge, it is wise to receive 
what is told us by those who know more than we do. 3 ^ut 
to knam anything requires mo re than this, and unless the 
reasons for any belief are so clear to our minds that we 
cannot doubt them, we have no right to say, w e know it to 
be true, but only that we h av e been told so. ? 

I think you can see how this rule of Descartes, that it 
is often more h onest to dou bt than t o be quite sur e without 
good grounds, would influence science. If scientific men 
in the time of Galileo, instead of saying c We know that a 
heavy weight falls more quickly than a light one because 
Aristotle said so,' had said more modestly, 4 We do not 
know, because we have never tried, but we think it probable 
Aristotle was right until some one shows us that he was mis- 
taken ;' — if they had gone to the Tower of Pisa in this spirit, 



w 



104 SEVENTEENTH CENTURY. ft. iil 

they would not have denied the truth of Galileo's experiment 
when it succeeded before their very eyes. A nd even no w, 
in jhe present dav. you will see that the greatest and be st 
m en who make the most discoveries, are those who ar e 
al ways willing to examine 'a new fact, even though it may 
co ntradict much that thev have, held before • an d who neve r 
pret end to know for certain anything which they have not 
studied w ith sufficient care to be convinced of its truth. 

Thus Bacon and Descartes both did great seivice to 
Science — Bacon by teaching that any true theory must be 
built up upon facts and careful experiments ; Descartes by 
insisting that it is more honest to acknowledge we are 
ignorant, and to wait for more light, than to pretend to 
know that which we have not clearly proved. 

Snellius Discovers the Law of Refraction, 1621. — 
Among other things, Descartes wrote much upon Optics, 
and you will often see it stated that he discovered th e law 
of refractio n. This law had, however, been laid down be- 
fore, in 1621, by a Dutch mathematician named Willebrord 
Sne llius, and Descartes only stated it more clearly. You 
will remember that the Arab Alhazen first pointed out that 
rays of light are bent or refracted when they pass from a 
rarer into a denser substance or medium (see p. 47), as for 
instance from air into water; and that the denser the 
medium is into which they pass, the more the rays are re- 
fracted. Vitellio and Kepler had measured some of the 
angles at which rays are refracted in water and glass, but 
they did not know of any law by which they could calculate 
how much any particular ray would be bent out of its course. 
For instance, in Fig. 12, suppose w w to be the surface 
of water in a glass vessel, upon which the rays a and b fall 
at the point o, and are refracted a to a' and b to b'. It is 
evident that b is bent much more out of its course than a, 



CH. XIII. 



THE LAW OF REFRACTION. 



[OS 



as you will see at once if you lay a straight ruler from end 
to end of each ray ; and if we were to draw other rays 
between these they would all be refracted at different 
angles, those being most bent which were farthest from the 



perpendicular. 




* Measurement of Refraction in Water. 

w w, Water, a a', b b', Rays passing from air into water, c c\ Line from the ray A 
to the perpendicular x , in the water, three-fourths the length of c c from the ray A 
in the air. d d' , d d, Similar lines from the ray B. 

Now in making telescopes it is very important to know 
how much each ray is refracted ; and as the rays are in- 
finite in number, it was impossible to know this unless some 
general rule could be found. Snellius set himself this task, 
and after a great number of very delicate experiments he 
arrived at a law which has proved to be always true. This 
law is best explained by the following experiment, which is 
not difficult to understand, although it is troublesome to 
perform it accurately. 

Draw a circle on a black board with an upright line x x 



io6 SE VENTEENTH CENTUR Y. pt. hi. 

through it, and then place the board upright in a vessel of 
water so that the surface of the water crosses the centre o. 
Then pass a ray of light through a tube so placed that the 
ray falls across the board in the direction a o ; it will then 
pass on through the water to some point a'. The line o a 
will now cut the circle at the point c, and the line o a' will 
cut it at c. From these two points draw horizontal lines c c 
and c c on the board to the upright line x x . Then if you 
compare the length of these two lines you will find that c c 
in the water is exactly three-fourths of c c in the air. 

Again, if you throw the light from your tube in the direc- 
tion b o, the result is the same. The length of d! d' in the 
water will again be three-fourths of d din the air. And this 
is equally true of all rays passing from air into water. When 
a vertical line is drawn through the point where the ray falls 
on the water, the tivo horizontal lines drawn to the place 
where the cii'de cuts the ray will always be in the same pro- 
portion, at whatever angle the ray strikes the water. There- 
fore, -f-ths is said to be the index of refraction for water, 
meaning that every ray which passes from air into water will 
have these two horizontal lines in the proportion of 4 to 3. 
In passing from air into glass they would always be in the 
proportion of 3 to 2, and every different substance, such as 
ice, amber, diamond, etc., has its own index of refraction. 
These have been calculated, and tables made, from which 
you can learn at once what is the index of refraction for 
any particular substance. 

It was this law of the proportion between the two hori- 
zontal lines in the air and in the denser substance which 
Snellius discovered, which is called after him ' SnelPsJaw.' 
It is expressed in mathematical language, thus :"' The ratj o 
between the sines of the incident and refracted rays is always 
the same for the same substance ;' sine being a mathematical 



CH. xiii. REFRACTION EXPLAINED. 107 

term for the measurement we have been making, which 
you will understand more fully when you have studied 
trigonometry. 



Chief Works consulted. — Herschel's ' Study of Natural Philosophy ;' 
Lewes's ' Biographical History of Philosophy ; ' Cuvier, ' Hist, des 
Sciences Naturelles;' Bacon, 'Novum Organum;' Huxley on ' Des- 
cartes,' Macmillan's Magazine ; ' Encyclopaedia Metropolitana,' art. 
* Light;' Herschel's 'Familiar Lectures,' art. 'Light.' 



io8 SEVENTEENTH CENTURY. pt. iil 



CHAPTER XIV. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Fabricius Aquapendente — Harvey discovers the circulation of the Blood 
— Gaspard Asellius — Pecquet — Riidbeck. 

Harvey's Discovery of the Circulation of the Blood, 

1619. — In the year 1600, when Galileo and Kepler were 
still at the beginning of their discoveries, a young English- 
man of two-and-twenty, named Harvey, who was born at 
Folkestone in 1578, went to Padua to study anatomy under 
the famous professor Fabricius Aquapendente. Although 
anatomists had by this time learnt a great deal about the 
bones and parts of a dead body, yet they were still very igno- 
rant about the working of a living one. They knew that 
arteries throb, as for example the pulse in the wrist, which is 
an artery ; and that veins (that is, the blue branching tubes 
which you can see under the skin in your hand and arm) 
contain blood and do not throb like the arteries ; but they 
had no clear idea of the use of either arteries or veins. 
jjVesalius had believ ed, like Arist otle, that the arteries con- 
tained chiefly a kind of air called ' vital spirits/ which they 
carried from the heart to all parts of the body ; and that 
the blood was pumped backwards and forwards from the 
veins to the heart by the act of breathing. A Spaniard 
named Servetus, an Italian named Columbus, and the 
botanist Csesalpinus, who all lived in the sixteenth century, 



ch. xiv. THE CIRCULATION OF THE BLOOD. 109 

had indeed suggested that blood from the heart flowed 
through the lungs (or the part we breathe with), and came 
back again to the heart ; and Caesalpinus had even noticed 
that if you tie up a vein it swells on the side of the bandage 
away from the heart; but the notions of all these men 
were very vague and unsatisfactory. 

The subject remained quite obscure till, while Harvey 
was studying at Padua, his master Fabricius discovered that 
many of our veins have curious valves inside them, made 
by the folding of the lining of the vein. These valves, which 
are just like little transparent pockets, lie open towards the 
heart so long as the blood is flowing in that direction ; but 
if you press on a vein — in your arm for instance — and 
force the blood away from the heart towards the fingers, the 
valves close at once, and the vein swells up because the 
blood cannot flow on. 

Fabricius thought that the use of these valves was merely 
to prevent the blood escaping too quickly into the branches 
of the vein ; but this explanation did not satisfy Harvey, and 
he determined to try to discover which way the blood 
moved in the different vessels which held it. In order to 
do this he laid bare the artery of a living animal, say in its 
leg, and tied it round tight, so that the blood could not flow 
past the bandage. He found that the artery became very 
full of blood and throbbed strongly above the place where he 
had bound it, but in the lower part of the leg it did not 
throb at all. This proved to him that the blood in the 
artery was flowing from the heart to the leg of the animal, 
and was stopped on its way down by the bandage. He then 
tied up a vein in the same way, and this time the swelling 
was in the lower part of the leg, below where the vein was 
tied. Therefore it was clear that the blood in the vein was 
flowing from the leg to the heart, and was stopped from flow- 



no SEVENTEENTH CENTURY. pt. lit 

ing upwards by the bandage. When he tied an artery and 
a vein in the arm the same thing happened ; the blood 
in the artery was flowing towards the hand, while in the 
vein it was flowing from the hand towards the heart. 

This led Harvey to suspect that the blood is always 
making a continuous journey round and round, first out of 
the heart through the arteries to all parts of the body, and 
then back through the veins to the heart again. And now 
the use of the little valves became evident. While the 
blood flows, as it should do, towards the heart, they lie open 
and offer it no resistance, but directly anything drives it in 
the wrong direction they close at once, and prevent it from 
flowing backwards. The throbbing of the arteries was also 
explained by this theory, for the blood being pumped into 
them by a regular movement of the heart, they swell at each 
rush of blood, and contract again before the next, and so 
rise and fall in exact time with the beating of the heart. 

Harvey also found that Csesalpinus and his contempo- 
raries had been right in suspecting that the blood makes a 
small circuit from the heart through the lungs and back 
again. We will try to understand all this with the assist- 
ance of a diagram, which, however, you must remember is 
only to help you, and not a real drawing of the parts. 
Starting from the left lower chamber a of the heart, the 
blood is pumped out of the left top corner of this chamber 
into an artery in the direction of the arrow i. This artery 
soon divides into two branches, one going downwards by 
the arrow 2 to the lower part of the body, the other upwards 
by the arrow 2 to the arms and neck; and, after flowing 
into the different parts of the body, the blood in the lower 
artery returns by the lower vein, 5, 6, 7, while the blood of 
the tipper artery is returning by the tipper vein 4, and both 
streams pour into the right upper chamber of the heart, b. 



ch. xiv. DOUBLE CIRCULATION OF THE BLOOD. in 



NECK 



The blood has now made one round, during which its 
colour has been changed from a bright scarlet to a dark purple, 
in consequence of its having parted with oxygen and gained 
carbonic acid in its passage through the different parts of the 
body. But it does not stop here. 
It escapes through a valve down 
into the lower chamber c ; out of 
the right top corner of which it 
starts again in the direction of 
arrows 8 and 9, and passes through 
the lungs, returning by the lung- 
veins, or pulmonary veins as they 
are called, in the direction of 
arrow 10, back into the left top 
chamber of the heart d. During 
this second journey it is acted 
upon by the air in the lungs and 
rendered pure and bright again by 
taking in fresh oxygen. It then 
passes down from d into the 
chamber a, from which it first 
started, and the whole round 
begins again. The first journey 
of the blood round the whole 
body is called the general circula- 
tion, and the second journey through the lungs is called the 
pulmonary circulation ; when Harvey had traced these two 
journeys he had proved the double circulation of the blood. 

Altho ugh this discovery as stated here appears very /Va*»/w, 




Fig. 13. 

Diagram of Heart and Blood-vessels 
seen from the front. 

a c, Lower chambers of the heart, 
called ventricles, b d, Upper 
chambers of the heart, called 
auricles. The arrows and num- 
bers show the course of the 
blood. 



simple, yet it took Harvey nineteen years to trace the blood ^^"^ * ' 
through all the channels of the body, before he felt quite ^- Ct ^J_ 
certain that he had hit upon the truth. Meanwhile he had/^^J.J! 
returned to London, and had been made physician at St. jL&£U-~> 



112 SEVENTEENTH CENTURY. pt. III. 

Bartholomew's Hospital. Here he taught his theory in his 
Lectures of 1 6 1 9, and at last published a small book on the 
circulation of the blood in 1628. Yet none of the older 
physicians would believe he was right, and Harvey told a 
friend that he lost many patients in consequence of his new 
doctrine. It is greatly to the credit of the unfortunate King 
Charles L, who was reigning at this time, and whose private 
physician Harvey was, that he gave him many opportunities 
of making physiological experiments on the animals in the 
royal parks, and took great interest in his discoveries. 

I Harvey wrote several other valuable books, and traced the 
(development of the chicken in the egg. He was of a very 
gentle and modest disposition, and disliked controversy so 
much that he could scarcely be persuaded to publish his 
later investigations when he found what disputes were occa- 
sioned by his great discovery of the circulation of the blood. 
He died in 1657, in his eightieth year. 

Discovery of the Vessels which carry Nourish- 
ment to the Blood, 1622-1649. — Hary ey^s doctrin e of 
the cir culation of the blood_ was t he real starting-p oint of 
^physiology , or the science of living bodies, and when the true 
action of the arteries and veins was known, many other 
vessels of the body were soon better understood. The 
most important of these were the vessels which carry nourish- 
ment from all parts of the body to make fresh blood. In 
■j^fjLoXfi . 1622 Gaspard Asellius, Pr ofessor of Anatomy at Pavia, saw 
a white fluid flowing from some thread-like tubes in the 
body of a dog which he was dissecting. This dog had been 
eating food just before he died, and Asellius found that the 
fluid came from the intestines and was the nourishing matter 
of the food. He called these fine tube s^/actea/s , because 
the fluid in them looked like milk. Some years later, in 
1647, Jean Pecquet, an anatomist of Dieppe, discovered 



CH. xiv. FURTHER PHYSIOLOGICAL DISCOVERIES. 113 

that thes e lacteals emp ty the mselves into a lar^e tub e called 
the th oracic duc t, which carries the fluid into the principal 
vein, and so to the heart; and finally, in 1649, a Swede 
named Olaus Rtldbec k discovered an immense number of 
fine thread-like tubes running from all the principal parts of 
the body, and carrying nourishing matter to the thoracic 
duct, and so through the great vein to the heart. He called 
these tubes lymphatics .• but in reality the lymphatics and 
lacteals are the same vessels, coming from different parts of 
the body and supplying the material for new blood. It is 
easy to understand that when physiologists knew not only 
how the blood circulates through the body, but also how a 
fresh supply of blood is being constantly provided, they had 
made a great step towards tracing out the workings of a 
living body. 

Chief Works consulted. — Sprengel, 'Hist, de la Medecine,' 181 5; 
Harvey's 'Anatomical Exercises,' 1673; Aikin's ' Biog. Mem. of 
Medicine till the Time of Harvey,' 1780 ; Huxley's ' Elementary Phy- 
siology j Carpenter's ' Physiology ; ' Kirke's ' Physiology j ' Cuvier, 
'Hist, des Sciences, etcj' D'Orbigny, 'Diet, des Sciences.' 



114 SEVENTEENTH CENTURY. pt. III. 



CHAPTER XV. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Torricelli — Perrier — Pascal — Otto Guericke — Foundation of Royal 
Society of London and other Academies of Science. 

Torricelli's Invention of the Barometer, 1644. — We 
must now turn to quite another subject on which new light 
was being thrown at this time. Among the many different 
mechanical experiments which Galileo made during his life, 
there had been one with a common pump which puzzled 
him very much, and which he had never been able to 
explain. 

You know that if you put the mouth of a squirt in water 
and pull back the handle, the water rises up into the tube. 
That is to say, as soon as you leave a space inside the squirt 
quite empty without any air in it, the water rushes in. 
In the same way, water may be made to rise up a long 
tube standing with its open end in a pond or basin, by 
drawing up a tight-fitting stopper a, Fig. 14, called a piston, 
and so driving the air out at the top and leaving a vacuum 
inside the tube. But Galileo noticed that as soon as the 
water had risen up to the height of about 34 feet it would 
not mount any higher, even though the tube between the 
surface of the water c, and the piston a, had no air in it. 
He could not, however, find out why the water should stop 
rising just at this point, and it was not till after his death 



TORRICELLI THE BAROMETER. 



"5 






Uftet 



that his friend and follower Torricelli (born 1608), who was 
a mathematical professor at Florence, hit upon the reason. 

Torricelli asked himself, 
'Why does the water rise in 
the tube at all? something 
must force it up.' Then it 
occurred to him that air must 
weigh something, and that it 
might be this weight on the 
open surface of the water which 
forced the water up the pump 
where there was no air press- 
ing it down. To understand 
this you must picture to your- 
self all the air round our 
globe to be pressing down 
upon the surface of the 
earth. Now, so long as the 
tube also is full of air the 
surface of the water will all 
be equally pressed down, and 
so will remain at one level 
at w b w. But when the pis- 
ton a is drawn up, it pushes 
the air above it out of the tube, and so lifts the weight off 
b, the water at which will immediately be forced up the 
tube by the pressure of the air on the water outside from w 
to w. This will go on till the water has risen about 34 feet 
to c, and then the column of water c b in the tube will 
press as heavily on the water at b as the air does on the 
water outside from w to w, so all the water w b w will 
again be equally pressed upon, and no further rise will take 
place in the tube. 
7 




Fig. 14. 

Section of a Suction-tube. 

Tight-fitting piston. c, Greatest 
height to which the water will rise, 
w b w, Natural level of the water. 



n6 



SEVENTEENTH CENTURY. 



PT. III. 





When Torricelli had come to this conclusion it occurred 
to him that if it was really the weight of the air which sup- 
ported the column of water, it ought to lift mercury or 
quicksilver, which is fourteen times heavier, to one-four- 
teenth of the height. So he took some mercury, and filling 
a tube a, about 34 inches long, with it, he turned the tube 
upside down into a basin of mercury, which being open was 

under the pressure of the atmo- 
sphere. The mercury began 
at once to sink in the tube, 
and finally settled down at b, 
about 30 inches above that 
in the basin. This was a 
beautiful experiment, and pro- 
ved almost to demonstration 
that the weight of ordinary air 
is sufficient to keep a column 
of mercury at a height of 30 
inches in vacuum. He had 
now therefore made an instru- 
ment which would measure the 
weight of the air, and as our 
atmosphere varies in weight ac- 
cording as the weather is cold 
or hot, or damp or dry, a 
column of this kind would 
be higher when the air was 
heavy, and lower when it was 
light. He kept this apparatus 
always in one place, and when the mercury rose above the 
30 inches he concluded that the air outside was heavy; 
when, on the contrary, it sank, this showed him that the air 
was light. When once this was discovered it was easy to 




Fig. 15. 
Torricelli's Experiment (Ganot). 



THE THERMOMETER. 



117 



mark off inches and parts of inches on the side of the tube, so 
as to reckon how much the mercury rose and fell each day. 

This was the beginning of the barometer, by (S> s 

which we measure the weigh t o f the atmosphere . 
It was a long time before people would believe 
that anything so invisible as air could affect the 
mercury, but this was at last c learly prov ed by 
a man named Perrier, who carried a baro- 
meter to the top of a mountain called the Puy 
de Dome, in Auvergne. As the summit of a 
mountain reaches to a great height in the atmo- 
sphere, it has, of course, less air resting upon 
it than the valley below has, and so the mer- 
cury when carried to this height not being 
pressed so much up the tube, fell nearly 3 
inches, and then rose again gradually as M. 
Perrier came down into the valley below, where 
there was a greater weight of air. This ex- 
periment, which was suggested by the famous 
French writer Pascal, confirm ed Torric elli's theory, 
and proved beyond doubt that it was the w r eight 
of the air which caused the mercury to rise. 

If now, after reading this account, you go 
and look at an ordinary upright barometer (Fig. 
16), you will perhaps be puzzled by finding it 
all enclosed in wood, and you will ask how the 
air can get to the mercury to press it down ; 




Fig. 16. 



but if you look carefully at the wooden box at Ordinary upright 
the bottom, you will find a small hole in the TT7 ar ° meer '. 

J A, Wood covering 

wood, often having a small plug of paper in it cup of mercury. 
to keep out the dust, and through this hole, ^SctaSf 
even stuffed up as it is, the pressure of the air 
can act. The space between the top of the column of 



u8 SEVENTEENTH CENTURY. pt. hi. 

mercury (b, Fig. 15) and the end of the tube is a vacuum, 
or a space with scarcely any air in it, and is still called a 
Torricellian vacuiwi. 

Invention of the Thermometer. — The date of the 
invention of the thermometer (or instrument to measure 
heat) is so uncertain that it will be best to speak of it here 
in connection with the barometer. Galileo is said to have 
made the first thermometer, which was simply a tube with 
a bulb at the end standing upside down in a basin of water. 
The bulb was filled with air, and when heat was applied to 
it, it expanded and drove back the water in the tube. A 
few years afterwards a Dutchman named Drebbel made 
thermometers with spirits of wine in them, and finally, in 
1670, mercury was used. Mercurial thermometers have 
the bulb and part of the tube filled with mercury, and the 
rest of the tube is quite empty, all the air being driven out 
by heating the mercury till it completely fills the tube, and 
then melting the end so as to close it. When the mer- 
cury cools it contracts and a vacuum is left above it. After- 
wards, when the bulb of this thermometer is heated, the 
mercury expands and rises in the tube ; when it is chilled 
it contracts and falls. 

The thermometer was not of any great use till early in 
the eighteenth century, when three men, Fahren heit, Celsius, 
and Reaumur, measured off the tube into degrees, so that 
the exact rise and fall could be known. Celsiu s and 
Reau mur took the melting point of ice as zero or o° of their 
scale, but Fahrenheit took his from a mixture of snow and 
salt, which was the greatest cold he knew how to obtain. 
For this reason 32 is the freezing point of water in a 
Fahrenheit thermometer, and his other divisions are different 
from those of Celsius or Reaumur. Celsius's scale is the 
one now used all over the Continent, and scientific men 



CH. XV. 



GUERICKE THE AIR-PUMP. 



119 



wish to introduce it into England, because it is so much 
more simple than Fahrenheit's. It is called ' centigrade,' 
or a hundred steps, because the tube is so divided that 
there are exactly ioo° between the freezing and the boil- 
ing point. 

Otto Guericke invents the Air-pump, 1650. — The 
Torricellian vacuum in the barometer was made, as we have 
seen, by simply filling a glass tube more than 30 inches 
long with mercury, and then turning it upside down into a 
basin of the same, so that the mercury in 
the tube fell to 30 inches, and an empty 
space was left at the top. But in 1650, 
a very few years after Torricelli's experi- 
ment, Otto Guericke, a magistrate of 
Magdeburg, in Prussia, made another step 
in advance and invented the air-pump, 
an apparatus by which air can be drawn 
out of a vessel, leaving it almost empty. 
Fig. 17 is the simplest kind of air-pump, 
and the way it works is not difficult to 
understand. At the bottom is a glass jar 
which has a round barrel or cylinder 
b b, fixed on the top of it. In the cylin- 
der is a tight-fitting piston, c c, like the 
one in the suction-tube p. 115, only that 
this one has in it a valve or door, d. 
There is also another valve, <?, at the place 
where the cylinder and glass jar meet, 
and both these valves open upwards. Now suppose we 
start with both valves shut and the piston c c down at the 
bottom of the cylinder resting on the valve, e. Then if we 
pull the piston gradually up, the valve d will be kept shut 
by the air outside pressing upon it, and so the piston will 




Fig. 17. 

Air-pump (Knight). 

b b, Cylinder. 

c c, Piston with valve. 

d e, Valves opening 

upwards. 



> 



120 SEVENTEENTH CENTURY. pt. in. 

drive the air between b and b out of the top of the 
cylinder. If the valve e remained also shut there would now 
be a vacuum, or space without air, in the cylinder b ; but 
this will not be so, because the air in the jar below, being 
no longer kept down by air above it, will expand, and 
forcing up the valve e will fill the whole of the jar and the 
cylinder with expanded air. 

Now bring down the piston c c again and observe what 
will happen. The thin air in the cylinder will be pressed 
down upon the valve e and will shut it, and then, not being 
able to get down into the jar, it will force up the valve d 
again, and escape out at the top. The piston will now be 
resting once more upon the valve e ; but the glass jar will 
have much less air in it than it had at first, because it will 
have lost all that which went up into the cylinder and was 
pressed out at the top. You have only to repeat this 
process and more air still will be drawn out, and thus by 
moving the piston up and down you gradually empty the 
glass jar. You cannot get quite all the air out, because 
there must be enough left to push open the valve e when 
you pull the piston up, but you can go on till there is very 
little indeed. Air-pumps are now constructed, by which all 
but an infinitesimal quantity of air can be drawn out and 
a vacuum left which is almost perfect ; but we are speaking 
of the one Guericke made, which was like the one I have 
described, only more complicated, and he worked it under 
water to make quite sure that no air should creep in at the 
cracks. 

The Experiment of the Magdeburg Hemispheres. — 
The first experiment which Guericke made with his air- 
pump was to prove that the atmosphere round our earth is 
p ressing do wn upon us heav ily and equall y in a ll directions. 
To do this he took two hollow metal hemispheres, like the 



CH. xv. THE FIRST ELECTRIC MACHINE. 121 

two halves of an orange with the inside taken out. These 
hemispheres fitted tightly together, so that no air could pass 
in or out when they were shut. Outside he fastened rings 
to hold by, so as to pull them apart, and at the end of one 
hemisphere he fixed a tap which fitted on to his air-pump. 
Now, as long as there was air inside the closed globe the 
two halves came apart quite easily ; but when he had drawn 
out the air with the air-pump and turned off the tap so as to 
leave a vacuum inside, it required immense strength to drag 
the globe into two parts. . This showed that the atmosphere 
was pressing heavily on every side of the globe, forcing the 
two halves firmly together, and as there was no air inside to 
resist this pressure, the person trying to separate them had 
to force back, as it were, the whole weight of the atmosphere 
to get them apart. As Guericke was burgomaster of 
Magdeburg, this experiment has always been called ' the ex- 
periment of the Magdeburg hemispheres.' 

The first Electrical Machine made by Guericke. — 
You will remember that Gilbert had shown in 1600 that 
sulphur and many other bodies, when they are rubbed, will 
attract light substances. Since his time very little notice 
had been taken of this fact, till Gueric ke invented the first 
ro ugh electrica l machine i n_i672. He made a globe of 
sulphur which turned in a wooden frame, and by pressing a 
cloth against it with his hand as it went round he caused 
the sulphur to become charged with electricity. His 
apparatus was very rough, but it led to better ones being 
made; and some years later, in 1740, a man named 
Hawksbee substituted a. glas^jflobe for the sulphu r and a 
piece . of silk fo r the clot h, and in this way electrical 
machines were made much like those we now use. 

Guericke also discovered that bodies charged with the 
same kind of electricity repel each other. If you hang a 



122 



SEVENTEENTH CENTURY. 



PT. III. 



piece of paper, or better still, a pith ball a, upon a silk 
thread b, and hold near to it a piece of sealing-wax c rubbed 
with dry flannel, you will find that the ball will at first be 
attracted towards the sealing-wax as in i, Fig. 18, but after 
a few moments it will be repelled and will draw back as in 
2 ; nor will it approach the sealing-wax again till it has been 
near to some other body, and given the electricity it has 
received. Thus an electrical body, as Guericke pointed 
out, attracts one that is not electrified, but repels it again as 
soon as it has filled it with electricity like itself. He was 







Pith-ball attracted and repelled by rubbed sealing-wax. 

also the first to notice the spark of fire and crackling sound 
which are produced by electricity when it passes between two 
bodies which do not touch each other. 
// Foundation of the Royal Society of London and 
// other Academies of Science, 1645. — We must now return 
to England, where about this time a society was founded, 
which, though it seemed insignificant at the time, had in the 
end a great influence upon science. In the year 1642 the 
unfortunate King Charles I. began that civil war with his 
people which ended in his being beheaded on January 30, 
1649. During these years all England was in a state of 
turmoil and confusion, and in London especially the riots 
and disturbances made it almost impossible for quiet and 
studious people to live in peace. It was under these cir- 



ch. xv. FOUNDATION OF THE ROYAL SOCIETY. 123 

cumstances that a small group of scientific men, among 
whom were Robert Boy le, son of the Earl of Cork, and Dr. 
Hooke, an eminent English mathematician, began to meet 
together privately to try and forget public troubles in 
discussing science. They assembled first in Londo n in 
1645, but soon mo ved to Oxfo rd to be out of the way of the 
constant riots, and continued to meet there till 1 662, after 
the restoration of Charles II., when they settled in London 
and fonned themselv es into a regular Society under a 
charter from the king. 

This was the beginning of the Royal Society of London, 
which has done so much for science during the last two 
hundred years, and which is still the leading scienti fic 
soc iety of Eng land. The following account of its early 
meetings is thus given by Dr. Wallis, one of the first mem- 
bers, ' Our business,' he says, ' was (precluding matters of 
theology and State affairs) to discourse and consider of 
philosophical enquiries, and such as related thereunto : as 
Physick, Anatomy, Geometry, Astronomy, Navigation, 
Staticks, Magneticks, Chymicks, Mechanicks, and Natural 
Experiments ; with the state of these studies, and their 
cultivation at home and abroad. We then discoursed of the 
circulation of the blood, the valves in the veins, the venae 
lactam, the lymphatic vessels, the Copernican hypothesis, the 
nature of comets and new stars, the satellites of Jupiter, the 
oval shape (as it then appeared) of Saturn, the spots on the 
sun and its turning on its own axis, the inequalities and 
selenography of the moon, the several phases of Venus and 
Mercury, the improvement of telescopes and grinding of 
glasses for that purpose, the weight of the air, the possibility 
or impossibility of vacuities and Nature's abhorrence thereof, 
the Torricellian experiment in quicksilver, the descent of 
heavy bodies and the degrees of acceleration therein, with 



124 SEVENTEENTH CENTURY. pt. in. 

divers other things of like nature, some of which were then 
but new discoveries, and others not so generally known and 
embraced as they now are ; with other things appertaining 
to what hath been called the New Philosophy, which, from 
the times of Galileo at Florence and Sir Francis Bacon 
(Lord Verulam) in England, hath been much cultivated in 
Italy, France, Germany, and other parts abroad, as well as 
with us in England.' 

How well we can picture from this account (written in 
1696), the pleasure which this little group of men, weary of 
the quarrels and bloodshed of the times, felt in discussing 
and investigating those laws of nature which seem to bring 
us into the calm presence of an Almighty Unchanging 
Power far above the petty wranglings of man ! The Royal 
Society has become, as I have said, one of the grandest 
scientific bodies in the world ; but it has probably never 
held more earnest or enthusiastic meetings than in the small 
lodgings at Oxford where it first took its rise in the midst 
of civil war. 

England was not long the only country which had a 
scientific society. Italy had already had two in the time of 
Galileo and Torricelli, but they had soon been broken up 
again. In Germany, the 'Imperial Academy of the Curious 
in Nature' was founded in 1662 ; and in 1666 the famous 
' French Academy of Sciences' was legally established by 
the French Government in Paris. 

All these societies were a great help in spreading the 
knowledge of scientific discoveries. Men who before were 
unable to publish what they knew, now sent or read their 
papers to those who could understand and appreciate them. 
The Royal Society began from the first to publish useful 
memoirs in their Philosophical Transactions; and in 1669, 
we find them bringing out the works of an Italian anatomist,) 



CH. XV. EARLY MEMBERS OF THE RO YAL SOCIETY. 125 

Malpighi, of whom we shall speak presently, and who sent 
to them works which he could not afford to publish in Italy. 
By this means the information scattered about the world 
was gathered together, and men were encouraged to seek 
out new truths when there was a chance of their being 
known and appreciated. 

Among the earlier members of the Royal Society there 
were some whose discoveries we must now consider. These 
were Boyle and Hooke, whom we have already mentioned ; 
Toh n Mayow , whose experiment s in chem istry are especially 
interesting ; Ray, Grew, and Malpighi, naturalists and ana- 
tomists ; the Dutch astronome r Huyghens ; the English 
astronomer Halley, and last, but not least, England's great 
philosopher, Sir Isaac Newton. 



Chief Works consulted. — Ganot's ' Physics,' 1873 ; Balfour Stewart 
on 'Heat,' 187 1 ; Rossiter's 'Physics,' 1870; Baden Powell's ' His- 
tory of Nat. Philosophy,' etc. ; Cuvier, ' Histoire des Sciences,' etc.; 
Birch's ' Hist, of Royal Society 3' Thomson's ' Hist, of Royal Society,' 
1812. 



126 SEVENTEENTH CENTURY. pt. m. 



CHAPTER XVI. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Boyle — Hooke — John Mayow. 

Boyle's Law of the Compressibility of Gases, 1661. 
— The Hon. Robert Boyle, seventh son of the Earl of Cork, 
and one of the principal founders of the Royal Society, was 
born in 1626. He had very delicate health, and when quite 
young travelled much abroad and learned there a great deal 
about science even before he was eighteen years of age. 
He was deeply interested in Galileo's discoveries, and was 
in Florence when that great astronomer died in 1642. 

After his return to England, when he was at Oxford, he 
read an account of Guericke's air-pump, and was so de- 
lighted with this new discovery that he set to work at once 
to make one without ever having seen the original. He 
succeeded so well, with the help of his friend and assistant 
Dr. Hooke, that his air-pump became famous, and many 
writers have by mistake given him the credit of being the 
inventor. We have seen, however, that Guericke was the 
first to hit upon this instrument ; Boyle only improved it, 
and made with it many very valuable experiments upon the 
weight and nature of air. These are too many and lengthy 
for us to examine here; but there is one law about the 
compression of gases which you will find connected with 
Boyle's name in all books on physics, and which you ought 



COMPRESSIBILITY OF GASES. 



127 



T7 



Pressure 

Atmospkere 
equals 



Pressure 

of 
Mercury 



■26 



-16 



A* 




to understand. Boyle knew from Torricelli's experiment 
that the weight of the atmosphere upon the air close down 
to our earth, is about equal to the weight of 30 inches of 
mercury in a tube (see p. 116). Now he wished to find out 
how much air is compressed, or forced into a smaller space, 
when more weight is put upon it, and to discover this 
he devised the following ex- 
periment. He took a tube a 1 , 
open at the long end and full 
of ordinary air, and by putting 
a little mercury into the tube 
and shaking it carefully till it 
settled at the bottom, he cut 
off a small quantity of air 
between b and c. This air 
was of course still under the 
usual weight of the atmo- 
sphere, which pressed down 
upon the mercury through the 
open end of the tube. But 
the mercury did not add to 
the weight because it stood 
at the same height on both 
sides of the tube, and so was 
evenly balanced. 

He next added more mer- 
cury, till it stood 30 inches 
higher in the long end than in the short one (as seen in a 2 ). 
The air between b and c was now pressed down twice as 
much as before, for it had the 30 inches of mercury weigh- 
ing upon it, as well as the atmosphere, which equalled 
another 30 inches. Boyle found that this double pressure 



4-J0 

-15 



30 



z-25 



M 



1S 



Fig. 19. 



had squeezed it into half the space (b c, Fig. a 2 ); in other 




i. 



128 SEVENTEENTH CENTURY. pt. ill. 

words, by doubling the fire sv/rp h.p. hn/f hnJwd Hip npfymp f 
the aiz . He then poured in 30 inches more mercury, 
making the pressure three times as great as at first, and he 
found the air was now compressed into one-third of the 
space it had filled at first. And this he proved to b e the 
la w of compre ssion of air and of all ga ses, that the volume of 
a gas (that is, the spac e it fills) is decreased in -proportion as the 
weight upon it i s increased. If you double the pressure youhalve 
the volume; if you halve the pressure you double the volume. 

This law of the compressibility of gases is known as 
Boyle's Law, or sometimes as Marriotte's La w, because a 
Frenchman named Marriotte also discovered it some years 
later without knowing that Boyle had done so. It is not 
always absolutely true, but we cannot stop to discuss the 
exceptions here; you will find them in books on physics 
and chemistry. 

Boyle and Hooke both gave much time to the study of 
chemistry. Hooke published a theory in 1665 t hat air a cts 
upon su bstan ces when they are heated, and so produces fire; 
for, said he, in making charcoal, although the wood is in- 
tensely heated and glows brightly, yet so long as the air is 
kept away it will not be consumed. Boyle also proved that 
a ca ndle will not bu rn, nor animal s breat he, without air. 
He found that when he put mice and sparrows into his air- 
pump, and then drew out the air, they died ; and that flies, 
bees, and even worms, became insensible; while fish, 
though they lived longer than the mice, soon turned on their 
backs and ceased to live. He also put a bird under a glass 
vessel full of air, and it died after three-quarters of an hour. 
It was clear, therefore, that fresh air is necessary to life, and 
Boyle began to think that just as a candle-flame cannot be 
kept up without air, so there must be some vital fire in the 
heart which is extinguished when air is shut out from it 



ch. xvi. JOHN MAYO W. 129 

This opinion he discussed at the Oxford meetings, and a 
young physician named Tohn Mavow listened very eagerly, 
and then went home and set himself to try and find out 
what this strange power in the air could be, without which 
neither fire nor animals could exist. 

Mayow's Experiments on Respiration and Com- 
bustion, 1645-1679. — John Mayow's private history is very 
short. He was born in Cornwall in 1645 ; he became a 
fellow of All Souls', Oxford, and practised as a physician in 
Bath ; and finally he died at the house of an apothecary in 
York Street, Coverit Garden, in 1679, before he was thirty- 
four years of age. This is all we know about his life ; but 
he must have been a diligent worker and a real lover of 
science, for though he died so young he left behind him an 
account of a number of experiments and discoveries which 
entitled him to be called the greatest chemist of the seven- 
t eenth centu ry. I wish we could go through all his 
experiments, for they form a most beautiful lesson of the 
earnest and painstaking way in which God's laws should be 
investigated. Mayow never made a careless experiment; he 
never thrust in his own guesses when it was possible to work 
out the truth ; he went on patiently step by step, taking 
every care to avoid mistakes, and never resting till he had 
got to the bottom of his difficulties. Let us now take some 
of his experiments on combustion, or burning, and respiration, 
or breathing, and try and follow them as carefully as he did. 

It seemed to him clear from the experiments of Boyle 
and Hooke 'that there must be something in the air which 
gave rise to flame and breath, and that this could only be a 
small part of the air, since a candle when put under a bell- 
glass went out long before all the air was gone. He first of 
all satisfied himself by experiments that this gas which 
burnt, and which he called fire-air, was not only in the 



130 



SE VENTEENTH CENTUR Y. 



PT. III. 



atmosphere, but existed in nitre, or saltpetre, and also in 
many acids ; and then he set to work to discover how much 
of it there was in ordinary air. To do this he took a piece 
of camphor, with some tinder dipped in melted sulphur, 
and placed it on a little platform hung inside a bell-jar (see 
Fig. 20). He then lowered the bell-jar into a basin of 
water, having first put a siphon or bell-tube under the bell- 
jar to let out enough air for the water to rise. Then he 
took the tube out, leaving the water at the same height 
inside and outside the jar, while the rest of the jar above 





Fig. 20. Fig. 21. 

Mayow's experiments on combustion and respiration (Yeats). 

the water was full of air. He now held up a burning-glass, 
and brought the sun's rays to a focus upon the camphor and 
tinder till it grew hot and burst into a flame. As it burnt 
he noticed that at first the water inside the jar sank down, 
because the air, being heated, expanded and took up more 
room. Then after a time the camphor ceased to burn, the 
jar cooled down, and the water rose again higher than before, 
till it stood above the water outside. The camphor was not 
all consumed, but when he tried to light it again he could 
not succeed. Why was this ? ' Because,' said Mayow, 
* there are no fire-air particles left in the jar to make the 



ch. xvi. RESPIRATION AND COMBUSTION. 131 

camphor burn, and the using up of these particles has made 
the rest of the air shrink and take up less space.' 

He now wished to compare burning with breathing, so 
he put a mouse in a cage and hung it inside the bell-jar, 
which he arranged over the water as before. Little by little 
as the mouse breathed the water crept up inside the jar, 
until when it had risen to a certain height the mouse drooped 
and died. It was clear, therefore, that animals in breath- 
ing use up some portion of the air. But is it the same 
portion which the flame uses ? Many people would have 
jumped at this conclusion, but Mayow was not content till 
he had proved it by another experiment. He put a lighted 
candle and a mouse together inside the bell-jar. The water 
now rose much faster than before ; the candle went out first, 
and then the mouse drooped as soon as the water had risen 
to the same height as in the other experiment. He was 
now certain that the candle and mouse both used up the 
same fire-air particles ; but to make still more sure, he put 
a candle under a bell-jar where the air had been spoiled by 
breathing, and it went out directly. 

His next step was to try whether air was lighter or 
heavier after the fii-e-air had been used up. To do this he 
put two mice into the jar, one at the top and the other at 
the bottom ; the one at the top drooped and died, while the 
other was still breathing. This proved that the air which 
had lost its fire-air particles was lighter and rose to the top, 
so that the top mouse could no longer breathe. By these 
and a great many other experiments Mayow prove d that air 
is made up of two portions — the one which support sjflame and 
life b eing compa ratively heavy ; and t he othe r light and use- 
less for burning or breathing : this last was the largest portion. 
I want you "to notice this particularly, because you will see 
by and by that Mayow had really discovered and described 



132 SEVENTEENTH CENTURY. pt. hi. 

two gases. The one which he called fire-air was oxygen, 
which was not known to other chemists for more than one 
hundred years later, and the other and lighter one is now 
called nitrogen. 

Having now proved that an animal in breathing uses up 
the same part of the air which a candle does in burning, 
Mayow wanted next to know what this fire-air did inside the 
animal. Harvey, as you remember, had proved that the 
blood passes through the lungs and there meets the air which 
we draw in at each breath. Here then, said Mayow, the 
fire-air particles must come in contact with the blood, and, 
joining with it in the same way as they do with the fat of a 
candle, must cause the heat of the blood. If any one wants 
to prove this let him run fast. He will find that he is 
obliged to breath more quickly and draw more air into his 
lungs, which will soon make his blood hotter and move 
more quickly, till his whole body glows with warmth. But 
if this mixture of the air with the blood does really take 
place, the arteries into which blood has just flowed from the 
lungs and heart ought to be full of air; and this is easily 
proved to be the case by putting warm arterial blood under 
an air-pump, where as soon as the pressure of the outside 
air is taken off, innumerable bubbles rise out of the blood 
as fast as they can come. 

/ In this way, by careful experiments and reasoning, Mayow 
I succeeded in proving that fire-air (or oxygen) is the chief 
\ agent in combustion and respiration. If he had not died so 
young he might have become more known, and men might 
have studied his discoveries, which he published in 1674. 
Unfortunately, however, he did not live to spread his know- 
ledge, and a false theory of combustion caused his work to 
be forgotten for many a long year. 

Theory of ' Phlogiston,' 1680-1723. — This theory was 



ch. xvi. THEORY OF ' PHLOGISTON.' 133 

proposed by two very eminent chemists, J ohn f oac fo m 
Tfrrf 1 ^ (1625-1682) and Ernest Stah l (1660-1734). 
Ernest Stahl in particular was a man of great talent and per- 
severance, and he did a great deal for the study of chemistry 
by collecting a great number of facts about the way in which 
different substances combine together, and by arranging these 
facts into a system. But his theory of combustion was a 
very misleading one, although it had a germ of truth in it. 
Stahl imagined that all bodies which would burn contained 
an invisible substance which he called ' Phlogiston] and that 
when a body was burnt it gave up its phlogiston into the 
air, and could only regain it by taking it out of the air or some 
other substance. It would only confuse you to try and 
understand how this theory explained some of the facts of 
chemistry. You will see at once one which it did not explain, 
namely, why a body should grow heavier when it is burnt, as 
Geber, 1500 years before, had shown it does. It seemed, 
however, to answer so well in a great many problems, that 
chemists believed in it for nearly a hundred years, and 
Mayow's true explanation was forgotten till the eighteenth 
century, when fresh experiments brought it again to the 
front. 

Chief Works consulted. — Brande's 'Manual of Chemistry' — Intro- 
duction ; Rodwell's ' Birth of Chemistry ; ' Yeats ' On Claims of 
Moderns to Discoveries in Chemistry and Physiology,' 1798; Birch's 
' Life of Boyle,' 1744 ; Shaw's ' Philosophical Works of Boyle,' 1725. 



i34 SEVENTEENTH CENTURY. pt. 1IL 



CHAPTER XVII. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 
Malpighi — Leeuwenhceck — Grew — Ray and Willughby. 

Use of the Microscope by Malpighi, 1661. — We have 
now fairly left behind us the first fifty years of the seven- 
teenth century; indeed, the experiments of Boyle and 
Mayow were all made after 1650. But I wish especially 
to remind you in this place that we have just begun the 
second half of the century, because it will help you to re- 
member an important study which began very quietly about 
this time, but which has in the end opened out to us an 
entirely new world of discovery. In the year i^6o£, at the 
beginning of the century, Galileo brought distant worlds into 
view by the use of the telescop e ; and in like manner in the 
year 1661, or about the middle of the century, Malpighi, 
by the use of the microscop e, revealed the wonders of infinitely 
mi nute structur es, or parts of living bodies ; enabling men 
to see fibres, vessels, and germs, which were as much 
hidden before by their minuteness as the moons of Jupiter 
had been by their distance. It is not quite certain who 
invented the compound microscope (fMKpbs, little ; a-Koirkm, 
I look at). Huyghens, who was born in 1 62Q, tells us 
that he was informed by eye-witnesses that his country- 
man Drehelius made them in 162 1, and this was probably 
about the time they were first used. Their application 



ch. xvii. FIRST USE OF THE MICROSCOPE. 135 

to the study of the structure of living beings we owe to 
Malpighi. 

Marcello Malpighi was born at Crevalcuore, near Bologna, 
in the year 1628; he became Professor of Medicine at the 
University of Bologna in 1656, and was early distinguished 
for his discoveries in Anatomy, made chiefly by the use of 
the microscope. It is not possible without a knowledge 
of anatomy, to understand thoroughly the structures which 
he described, but we may be able to form a general idea 
of the work he did. 

One of his first experiments was the examination of the 
general circulation of the blood in the stomach of a frog, etui - 
and he succeeded in de monstrating the fact that the arteries Ccd-uJ^ 
are connected with the vein s by means of minute tubes 
called capillaries , thus proving beyond doubt the truth of 
Harvey's doctrine. His next work was to study the passage 
of the blood through the lungs (see p. in), and to describe 
the air-cells from which the blood derives its oxygen. If 
you can get anyone to show you properly under the micro- ' 
scope a section of a frog's lung, you will see a number of 
round spaces bordered by a delicate partition; these are 
sections of air-cells, and round them you will see a network , 
of minute tubes. Through these tubes or capillaries the CU^ ^ 
blood flows in a living creature, and takes up oxygen from 
the air through the coverings or nmnbranes of the air-cells 
and capillaries, giving back carbonic acid in exchange to 
be breathed out into the atmosphere. Malp ighi was th e 
first to p oint out these air-ce lls, and to describe__theway in 
which the blood passes over them. After this he turned his 
attention to the t ongue , and p ublish ed in 166 5 a care ful d e- tirt/t Jr 
scription of all its nerves, vess els, and coverings. He also 
pointed out that the outside layer of the skin or epidermis 
of the ne .gro is as white as your s__or mine, and that the 



136 



SEVENTEENTH CENTURY. 



\ 




Fig. 22. 

Section of the Skin (Huxley.) 

Epidermis, b, Its deeper layer, or 
Malpighian layer, c, Upper part of 
the dermis, or true skin, d d, Per- 
spiration ducts. 



colouring matter which gives him his dark colour is con- 
tained in a deeper layer just at the point where the epidermis 

joins the dennis or real fib- 
rous skin beneath (see Fig. 
22.) This soft layer is st ill 
called the ' Malpighian layer,' 
and t he dirieren t colours of 
the skins of animals are 
caused by little cells of col- 
ouring matter which lie buried 
in it 

After Malpighi had exam- 
ined many other minute struc- 
tures of the human body, he began next to study insects, 
and in 1669 he published a beautiful description of the 
silkworm. With his microscope he discovered the small 
holes or pores which are to be seen along both sides of the 
body of an insect, and he found that these pores were open- 
ings into minute air-tubes, which pass into every part of 
the insect's body, and form a breathing apparatus. He also 
described the peculiar vessels in which the silkworm secretes 
the juice from which its silk is made, and he traced the 
changes which the different parts of the worm undergo as 
it turns into the moth. In fact , he was the first man wh o 
attemp ted to trace out the anatomy of such sm all creat ures 
a s inse cts : a study to which men now often devote their 
whole lives. 

But grand as Malpighi's discoveries were, a Dutchman 

<« - — ». named Leeuwenhceck (born 1632, died 1723) made the 

I microscope tell even a more wonderful tale, for he detected 

-r* N^^Hn water and in the insides of animals those extremely 

/ V A/VV ^ min^j-P hgings •rc hich he called anim alcules. He showed 

that a piece of the soft roe of the cod-fish not bigger than 



ch. xvii. VEGETABLE ANATOMY. 137 

an ordinary grain of sand might contain ten thousand of 
these living creatures. When such tiny beings as these 
could be seen and examined, I think you will acknowledge 
that I did not speak too strongly when I said that the 
microscope has opened out to us a new and marvellous 
world of life. 

Vegetable Anatomy. ^ Grew and Malpighi, 1670. — 
From insects Malpighi next turned to plants ; and it is 
curious that at about the same time an English botanist 
named Nehemiah Grew (born 1628, died 17 11), who was 
secretary to the Royal Society, also took up the same study ; 
and the papers of the two men were laid before the Royal 
Society on the same day in 1670. Malpighi's complete 
work was afterwards published in 1674, and Grew's in 1682. 

The investigations of these two men agreed in many 
remarkable points ; they had both of them examined with 
great care the flesh (if we may call it so) of plants, and 
they described for the first time the tiny bags or cells of 
which every part of a plant is made, and which you may 
easily see for yourself if you put a very thin piece of the v' Lie- 
pulpy part of an apple, or better still, of 
the pith of elder under the microscope 
(see Fig. 23). They had also noticed 
the long tubes which ne among "the 



kcJ* 




Fig. 23. 
Cellul.-ir tissue from the 



woody fibres in the stringy or fibrous 

part of a plant and in the veins of the 

leaves, and Grew had pointed out quite 

truly that th ese tu bes, which are called 

ves sels or ducts , are composed of pIth of the elder (° liver )- 

strings or cells which have grown together into one long 

cell or tube. 

Grew also first saw t hose beautiful little mouths in the 

skin of the leaves called stomatcs, which open when the air 




138 SEVENTEENTH CENTURY. pt. hi. 

is damp, and serve for taking in and giving out air and 
moisture. To see these you must take a very thin piece of 
the skin of the under part of the leaf, and place it in water 
under the microscope; you will see a 
number of very small roundish or oval 
spaces {a, Fig. 24), and if you watch 
carefully you will most likely see some 
of them open in the water. Grew dis- 
covered these stomates and pointed out 
their use. H e also studied ve ry carg >. 
Fig. 24. ^ f ully the way in which ^eedsbggi^ ..i-q_ 

Piece of the outer skin . T^^ — ~Z7^\ ~T . ,. , 

taken from the under- Spr OUt j DU t On thlS p oint Ma lpighl did 

a a, stomates. b, Cells the mo st, f or he wat ched under the 

of the skin (Carpenter). . . n . _ . 

microscope the wh ole pro cess of the 
growth of seeds, and des cribed air~the different states 
of the germ, comparing them to the growth of a chicken in 
the egg, and showing how much an egg and a seed resemble 
each other in many particulars. 

By these few examples you can form an idea how much 
Grew and Malpighi did towards the study of the structure 
of plants or Vegetable Anato?ny, a science which they may 
almost be said to have founded, and one which you may 
work at yourself with the help of a fairly good microscope 
and an elementary book on Botany. If you will do this 
with patience and care you will be well repaid ; for some of 
the most beautiful and delicate of the contrivances of Nature 
lie hid in those frail flowers which we gather for their scent 
and beauty, and fling away without imagining what wonder- 
ful structures they can reveal to us even when dead and 
withered. 

Classification of Plants and Animals by Ray and 
Willughby, 1693-1705. — We now come to the history of 
two friends, which is in itself a pleasure to dwell upon, even 



ch. xvii. ZOOLOGY. 139 

if they had not both been great men ; but which becomes 
much more interesting when we remember that it was their 
love of the study of Nature which first brought them together, 
and which made them inseparable, not only in life, but in 
their works after death. 

John Ray, one of the greatest botanists of the seven- 
teenth century, was born near Braintree, in Essex, in the 
year 1628. Though only the son of a blacksmith, he re- 
ceived a good education at the grammar school of the town 
and went afterwards to Cambridge, where he remained as a 
tutor after he had taken his degree. Here one of his first 
pupils was a Mr. Francis Willughby, of Middleton Hall, in 
Warwickshire, a man seven years younger than himself, and 
belonging to quite a different rank in society. These two 
men, however, had one great interest in common — they were 
both' passionately fond of Natural History, and spent all 
their spare time in studying it together. 

They soon found that the descriptions and classifications 
of plants and animals which had been drawn up by earlier 
naturalists were very imperfect, and they formed the project 
of making a complete classification of all known plants and 
animals, describing them as far as they were able, and 
arranging them in groups according to their different cha- 
racters. Willughby undertook the birds, beasts, and fishes, 
while Ray devoted himself chiefly to plants ; but they worked 
together in all the branches, and Ray, as we shall see, ended 
by doing far more than his share of the work. 

From 1663 to 1666 the two friends travelled together 
over England, France, Germany, and Italy, making collec- 
tions of plants and animals, and Willughby took a pleasure 
in using his wealth to add to the knowledge of his poorer 
companion. Soon after their return Ray was made a fellow 
of the Royal Society, and Willughby was not long before he 
8 



140 SEVENTEENTH CENTURY. pt. m. 

received the same honour. Willughby now married, and 
though Ray continued his travels alone, yet a great part of 
his time was spent at Middleton Hall, where the two friends 
made experiments upon sap in the trees and the way it 
flows. 

In this way they worked together till, in 1672, Mr. 
Willughby died of a fever, leaving a sum of sixty pounds a 
year to Ray, and begging him to bring up his two little sons 
and to continue his works on Zoology, which he had left un- 
finished. The way in which Ray fulfilled these requests fully 
showed the affection which he felt for his lost friend. He 
brought up the boys till they were removed from his care by 
relations ; and as to the works, he edited them with so much 
care and such a touching desire to give every credit to 
Willughby, that much of the work which must have been 
Ray's stands in his friend's name, and in fame, as in life, it 
is impossible to separate them. 

We can only form a very general idea of the kind of 
classifications which Ray and Willughby adopted, for a mere 
list of classes would be neither interesting nor useful. The 
first book, which was on Quadrupeds, was published by Ray 
in 1693. He divided these first, as Aristotle had done, 
into oviparous, or those that are born from eggs, like frogs 
and lizards ; and viviparous, or those which are born alive, 
like lambs and kittens. He then divided the viviparous 
quadrupeds into those which have the hoof all in one piece, 
like the horse, and those with a split hoof, like the ox and 
goat. Those with split hoofs he divided again according as 
they chewed the cud like the ox, or did not like the pig. 
Then came the animals whose hoofs are split into many 
parts, as the hippopotamus and rhinoceros ; then those which 
have nails only in place of toes, as the elephant ; then those 
which have toes but no separation between the fourth and 



ch. xvn. ZOOLOGY. 141 

fifth toes, as the cat, dog, and mole ; and lastly, those which 
have the fifth finger, or toe, quite separate, as the monkeys. 
After this he divided them more fully, by their teeth, and 
thus made a very fair classification of quadrupeds. 

The book upon Birds, which comes next in order, had 
already been published by Ray in 1677, four years after 
Willughby's death. In it birds we re d hdded Jkst into land- 
birgls and water-b irds, and were then classified by the shape 
of their beak and claws, and according as they fed upon 
flesh like the vulture, or upon fruit and seeds like the parrot. 
The water-birds were also divided into those which wereiQng- 
legged, as the flamingo, or short-leg ged, as the duck, and 
according as th e web between their toes was more or less 
co mplete . 

The ' History of Fishes ' is given as the joint work of Ray 
and Willughby; the groups into which they divided them 
are nearly the same as those now used. 

The ' History of Insects ' was Ray's work, and was pub- 
lished by friends after his death, in the same way as he had 
published Willughby's. He divided insects into — first, those 
which undergo metamorphosis (that is, turn from the cater- 
pillar into the moth), as the silkworm, and all moths and but- 
terflies ; and second, those which do not change their form ; 
and then he subdivided them according to the number of 
their feet, the shape of their wings, and many other characters. 

But Ray's greatest work was upon Plants, which he 
classified much more perfectly than Csesalpinus had done. 
He divided them first into wifi£rji£c t_pla?i ts, or those whose 
flo wers are invis ible, as mosses or mushrooms ; and perfect 
plants, or those having visible flowers. The perfect plants 
he divided into two classes — first, the dicotyled ons, or those 
whose seeds open out into two seed-leaves, like the wall- 
flower or the bean in which last you can see the two cotyle 



142 SEVENTEENTH CENTURY. pt. hi. 

dons very clearly as they form the two halves of the bean 
when you take off the outer skin ; and secondly, the 
7nonocotyledons, or those whose seeds have only one large 
seed-leafTlike a grain of wheat. The dicotyledons he again 
divided into those having simple flowers, like the buttercup, 
and those whose flowers are compound, like the daisy ; for if 
you pick a daisy to pieces you will find that the centre is 
made up of a number of little flowers, each of them perfect 
in itself and having its own green calyx and coloured corolla, 
and its own stamens and seed-vessel. Even the white strap- 
like rays round the daisy are each a separate though imperfect 
flower, therefore every daisy is a branch of little flowerets, or 
a compound flower. Ray went on next to class the simple 
flowers according to the number of seeds they bore, and the 
way in which the seeds were arranged in the seed-vessel. 
In this way he made a rough but complete classification of 
all the known plants. Linnaeus, the great botanist of the 
eighteenth century, ad opted many of Ray's divisions, which 
had meanwhile been made more perfect by Joseph Tourne- 
fort, a Frenchman, born at Aix, in Provence, in 1656. 

Ray outlived his friend Willughby more than thirty 
years, and died in 1705 at the age of seventy-seven. His 
death brings us to the end of the Natural History of the 
seventeenth century, so far as we have been able to notice 
it. But I cannot too often insist upon the fact that the men 
here selected — Malpighi, Grew, Ray, and Willughby — are 
merely a few among an immense number of observers in the 
same line of study. I have picked out those whose work 
is most easily to be understood, and whose names are well- 
known ; but I could have selected not four but forty others 
who ought to have been mentioned, in anything like a com- 
plete hist 017 of the period. We must, however, be content 
to catch here and there a glimpse of the advance that was 



ch. xvii. RAY'S CLASSIFICATION OF PLANTS. 143 

being made, always remembering that an almost inexhaust- 
ible store of further information remains behind when we 
have opportunity to seek for it 



Chief Works consulted. — Cuvier, 'Hist, des Sciences Naturelles ; 
Carpenter's ' Physiology ; ' Sprengel, ' Histoire de la Medecine ; ' 
Whewell's ' History of Inductive Sciences ; ' Carpenter, ' On the Micro- 
scope ;' ' Memorial of John Ray,' E. Lankester, 1846 ; ' Life of Ray 
and Willughby,' Naturalists' Library, vol. xxxv. ; Lardner's ' Encyclo- 
paedia ' — Classification of Animals. 



144 SE VENTEENTH CENTUR Y. pt. in. 



CHAPTER XVIII. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Newton — Fluxions and differential Calculus — Theory of Gravitation — 
Attraction varies inversely as the Squares of the Distance — The 
1 Principia,' 

Newton, 1642. — We must now leave the living creation and 
return to physical science, for, during all those years with 
which we have been occupied since the time of Galileo 
and Kepler, a boy had been growing up into manhood, who 
was to become one of the greatest men of science that Eng- 
land has ever known. In 1642, the same year in which 
Galileo died, a child was born at Woolsthorpe, near Gran- 
tham in Lincolnshire, who was so tiny that his mother said 
1 she could put him into a quart mug.' This tiny delicate 
baby was to become the great philosopher Newton. 

We hear of him that he was at first very idle and 
inattentive at school, but, having been one day passed in 
the class by one of his schoolfellows, he determined to regain 
his place, and soon succeeded in rising to the head of them 
all. In his play hours, when the other boys were romping, 
he amused himself by making little mechanical toys, such as 
a water clock, a mill turned by a mouse, a carriage moved 
by the person who sat in it, and many other ingenious con- 
trivances. When he was fifteen his mother sent for him 
home to manage the farm which belonged to their estate \ 



CH. xviii. Slid ISAAC NEWTON. 145 

but it was soon clear that he was of no use as a farmer, for 
though he tried hard to do his work, his mind was not in it, 
and he was only happy when he could settle down under a 
hedge with his book to study some difficult problem. At 
last one of his uncles, seeing how bent the boy was upon 
study, persuaded his mother to send him back to school and 
to college, where he soon passed all his companions in 
mathematics, and became a Fellow of Trinity College, 
Cambridge, in 1667. But even before this, in the year 1666. 
his busy mind had already begun to work out the three 
greatest discoveries of his life. In that year he discovered 
the remarkable mathematical process called the 'Methodjtf 
Fluxions] which is almost the same as that now called the 
1 D ifferential Calculus ,' worked out about the same time by 
Leibnitz, a great German mathematician. In that year he 
also made the discoveries about ZightandColour, which we 
shall speak of by and by ; and again in that year he first 
thought out the great Theory of Gravitation, which we must 
now consider. 

Theory of Gravitation, 1666. — In the course of his 
astronomical studies, Newton had come across a problem 
which he could not solve. The problem was this. Why 
does the moon always move round the earth, and the planets 
round the sun? The natural thing is for a body to go 
straight on. If you roll a marble along the floor it moves 
on in a straight line, and if it were not stopped by the air 
and the floor, it would roll on for ever. Why, then, should 
the bodies in the sky go round and round, and not straight 
forward? 

While Newton was still pondering over this question, the 
plague broke out in Cambridge in the year 1665, and he 
was forced to go back to Woolsthorpe. Here he was 
sitting one day in the garden, meditating as usual, when an 



146 SEVENTEENTH CENTURY. pt. iil 

apple from the tree before him snapped from its stalk and 
fell to the ground. This attracted Newton's attention ; he 
asked himself, Why does the apple fall? and the answer he 
found was, Because the earth pulls it. This was not quite a 
new thought, for many clever men before Newton had 
imagined that things were held down to the earth by a kind 
of force, but they had never made any use of the idea. 
Newton, on the contrary, seized upon it at once, and began 
to reason further. If the earth pulls the apple, said he, and 
not only the apple but things very high up in the air, why 
should it not pull the moon, and so keep it going round 
and round the earth instead of moving on in a straight line ? 
And if the earth pulls the moon, may not the sun in the 
same way pull the earth and the planets, and so keep 
them going round and round with the sun as their centre, 
just as if they were all held to it by invisible strings ? 

You can understand this idea of Newton's by taking a 
ball with a piece of string fastened to it, and swinging it 
round. If you were to let the string go, the ball would fly 
off in a straight line, but as long as you hold it, it will go 
round and round you. The ball does not come to you, 
although the string pulls it, because the sideway pull of the 
string cannot check its motion onwards, but only alters its 
direction. This it does at every moment, causing it to 
move in a circle round you. In the same way the moon 
does not come to the earth, but goes on revolving round 
it. 

Newton felt convinced that this guess was right, and that 
the force of gravitation, as he called it, kept the moon going 
round the earth, and the planets round the sun. But a mere 
guess is not enough in science, so he set to work to prove 
by very difficult calculations what the effect ought to he if it 
was true that the earth pulled or attracted the moon. To 



ch. xviii. NEWTON'S STUDIES. 



H7 



make these calculations it was necessary to know exactly 
the distance from the centre of the earth to its surface, 
because the attraction would have to be reckoned as if all 
the mass of the earth were collected at the centre, and then 
as decreasing gradually till it reached the moon. Now the 
size of the earth was not accurately known, so Newton had 
to use the best measurement he could get, and to his great 
disappointment his calculations came out wrong. The moon 
in fact moved more slowly than it ought to do according to 
his theory. The difference was small, for the pull of the 
earth was only one-sixth greater than it should have been : 
but Newton was too cautious to neglect this want of agree- 
ment. He still believed his theory to be true, but he had 
no right to assume that it was, unless he could make his 
calculation agree with observation. So he put away his 
papers in a drawer and waited till he should find some way 
out of the difficulty. 

This is one of many examples of the patience men must 
have who wish to make really great discoveries. Newton 
w aited sixteen years before he solv ed th e problem , or spoke 
t o anv one of the great thought in his mi nd But more 
light came at last ; it was in 1666, when he was only twenty- 
four, that he saw the apple fall; and it was in 1682 that he 
heard one day at the Royal Society that a Frenchman 
named Picart had measured the size of the earth very accu- 
rately, and had found that it was larger than had been 
supposed. Newton saw at once that this would alter all his 
calculations. Directly he heard it he went home, took out 
his papers, and set to work again with the new figures. 
Imagine his satisfaction when it came out perfectly right ! 
It is said that he was so agitated when he saw that it was 
going to succeed, that he was obliged to ask a friend to 
finish working out the calculation for him. His patience 



> 



148 SEVENTEENTH CENTURY. pt. hi. 



was rewarded; the attraction of the earth exactly agreed 
with the rate of movement of the moon, and he knew now 
that he had discovered the law which governed the motions 
of the heavenly bodies. 

This law of Newton's is called the i Law of Gravitation] 
and we must now try to understand what it is. Gravitation 
means the drawing of one thing towards another. All the 
objects upon our earth are held there by gravity, which pulls 
or attracts them towards the centre of the earth. If there 
were no such thing as gravity there would be nothing to prevent 
our chairs and tables, and even ourselves, from flying into space 
at the slightest impulse ; but they are all held to the earth by 
gravity, and if any object could pass freely through the ground, 
it would be drawn down with increasing velocity till it reached 
the earth's centre of gravity. Then its velocity would decrease, 
till, on reaching the opposite surface, it would be drawn again 
towards the centre, and move thus to and fro, unless friction 
at last brought it to rest at the earth's centre of gravity. 

Now let us see how this attraction of gravitation affects 
the planets. Every one of the bodies in the heavens pulls 
or attracts all the other bodies, just in the same way as the 
earth attracts the apple on the tree. But as they are all 
moving rapidly along (like the ball swung round your head) 
they do not fall into each other, but the smaller bodies move 
round the larger ones which are near them, just as if they 
were fastened to them by invisible elastic threads. The 
smaller ones move round the larger one, because it is not 
only each body as a whole which pulls the other bodies, but 
every tiny atom of matter in each planet is pulling at all the 
atoms in all the other planets ; so the bigger a body is, and 
the more atoms it has in it, the more it will draw other 
bodies towards it. Our sun pulls the planets, and the 
planets pull the sun ; but our sun has 700 times more atoms 



CH. XVIII. 



THE LAW OF GRAVITATION. 



149 



in it than all the planets put together, and so it keeps them 
moving round it. In the same way our earth has eighty 
times more atoms in it than our moon, and so it keeps the 
moon moving round it. 

In this way the force of gravity keeps all the different 
planets in their paths or orbits. It does not set them 
moving ; some other force unknown to us first started them 
across the sky — gravitation is only the force which determines 
the direction in which they move. 

It was a grand thing to have discovered this force, but it 
would have been of little value to Astronomy to know that 
the heavenly bodies attracted each other unless it could also 
be known how much influence they have upon each other. 
This also Newton worked out accurately. You will remem- 
ber that Kepler had shown that planets move in ellipses, 
having the sun in one of the two foci (see Fig. 10, p. 97). 
Knowing this, Newton was able to calculate how much the 
sun attracts a planet when it is near, and how much when it 
is far off, so as to make it move in an ellipse ; and he found 
that exactly as much as the square of the distance increases, 
so much the at 'traction decreases : 
that is, the attraction grows less 
and less at a regular rate as 
you go farther away from the 
body that is pulling. 

For instance,, suppose that 
at the point 1, Fig. 25, a planet 
was one million of miles away 
from the sun, and was being 
attracted with immense force. 
When it arrived at the point 
3 it would be about twice as far, or two millions of miles 
■distant ; and the square of 2 being 4(2x2 = 4), the attrac- 




Fig. 25. 



150 SEVENTEENTH CENTURY. pt. iil 

tion of the sun at this point will be only one-fourth as much 
as it was at the point i. At the point 7 the planet would 
be about three times as far, or three millions of miles from 
the sun, and as the square of 3 is 9 (3 x 3 = 9), the at- 
traction here will only be -£-th of the attraction at the point 1. 
And so the calculation goes on; if the planet went 12 
millions of miles off, the attraction would be T -J T what it 
was at first, and at 9 2 millions of miles the attraction would 
be -g-^eTj so tnat when the planet is very far away the 
attraction becomes very slight indeed, but it will never 
entirely cease. In scientific language this law is expressed 
by the words, The attraction varies inversely as the square of 
. the distance. When once this law was known, it explained 
in a most beautiful and complete way not only the three 
laws of Kepler, but all the complex movements of the 
heavenly bodies. These Newton worked out approximately 
by the help of his ' Method of Fluxions,' which enabled him 
to calculate all the varying rates at which the planets move 
in consequence of their mutual attraction ; and he showed 
that whenever we know clearly the position and mass of all 
the bodies attracting a planet, the law of gravitation accounts 
for the direction in which it moves. 

If you will consider for a moment what a labour it must 
be to calculate how much the different planets pull each 
other at different times — when they are near together and 
when they are far off, when they are near each other and 
near the sun, or near each other and far from the sun, in 
fact in all the different positions you can imagine — you may 
form some idea of the tremendous work he did. When he 
published his great book, the 'Principia,' in 1687, there 
were not more t han eight people in the world w ho were able 
to understand the full meaning of his calculations and 
thoughhis theory of gravitation was well 



ch. xviii. LAW OF GRAVITATION EXPLAINED. 151 

received, and his name became one of the most renowned 
and honoured in the world, yet it was more than fifty years 
before his work was thoroughly appreciated. 

It may therefore easily be imagined that it is not possible 
to give a simple sketch of what is contained in the 'Principia;' 
but some idea may perhaps be formed of the grandeur of 
the law of gravitation from an enumeration of some of the 
problems which Newton explained by its action. 

1. He explained those laws of motion which Galileo had 
proved by experiment, and showed that it is the force of 
gravity which causes th e weisrht of bodie s ; and determines, 
when combined with other laws, the rate at which they fall, 
and the path they describe. 

2. He worked out the specific gravity of the planet s, 
showing, for example, that the matter of which Saturn is 
composed is about nine times lighter than the matter of our 
earth. 

3. He showed how the attractions of the sun and of the 
moon cau se the tides of the sea , and worked out accurately 
the reason of the spring and neap tides. 

4. He proved that the earth co ujd not be a perfect globe , 
and m easured almost exactly h ow great the bulg e at the 
equator and the flattening at the poles must be. And this 
he did entirely by calculation, for no measurements had then 
been made, to lead any one to doubt that the earth was a 
perfect globe. 

5. He gave a co mplete explanation o f the cause of th e 
1 prece ssion of the equinoxes. ' the occurrence of which, as 
you will remember, Hipparchus had discovered (see p. 30). 

6. He not only sho wed why the planets moved in ellipses 
while a l ine joining \he. snn and a. planet cuts off e qual areas 
in equal times ; but he als o accounted for many irregularities 
in these movements, arising from their mutual attractions, 



152 SEVENTEENTH CENTURY. pt. hi. 



thus showing that gravitation explains not only the general 
laws but even apparent exceptions. 

7. Of all bodies comets are apparently the most irregu- 
lar, yet Newton calculated that they probably move in a 
peculiar curve called j^Jiarabola, which is represented by the 
section of a cone cut parallel to one of its sloping sides, and 
since his time it has been proved that the motions of some 
comets can be sufficiently well explained by this theory, 
while others move in ordinary ellipses like the planets, and 
return periodically. These and many other problems of the 
universe Newton showed could all be referred to the action 
of gravitation ; and he concluded his work with a grand 
description of the mechanism of the heavens, dwelling with 
deep reverence upon the thought of that Infinite Mind 
which gave rise to such a wonderful and comolex machinery, 
.working in perfect order. 



Chief Works consulted. — Brewster's 'Life of Newton;' 'Lives of 
Eminent Persons' — Lib. of Useful Knowledge; Airy's ' Elementary 
Astronomy ;' Airy, ' On Gravitation,' 



CH. xix. TRANSITS OF MERCURY AND VENUS. 153 



CHAPTER XIX. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Transits of Mercury and Venus — ^Gassendi — Horrocks — Halley — 
Explanation of Kalley's Method. 

First Transits ever observed of Mercury and Venus, 
1631-1639. — We must now pause for a moment before 
passing on to Newton's discoveries in Optics, in order to 
mention a remarkable astronomical suggestion made about 
this time by the astronomer Halley (born 1656, died 1742), 
who was the friend and disciple of Newton. 

You cannot fail to have heard and read something about 
the expeditions sent in December 1874 to all parts of the 
world to observe the Transit (or Passage) of Venus across 
the sun. The object of these observations was to measure 
the sun's distance from the earth ; and Halley was the first 
to propose this method of measurement, in 1691, and to 
show how it might be accomplished. 

It is well known that as the two planets Mercury and 
Venus are nearer to the sun than our earth is, they are con- 
stantly passing between us and it. But usually they pass 
either below or above the sun, and it is only rarely that they 
cross over the bright disc, so as to be seen through the 
telescope as a round black spot upon the sun's face. Withl 
Mercur y this happens at interv als of from seven to thirtee n | 
years ; but with Venus it is much more rare, for though two 
transits generally come together with an interval of only 



154 SEVENTEENTH CENTURY. pt. in. 

eight years between them, yet after this there is a gap of 
more than a hundred years before another transit occurs. 

After Kepler had finished the famous Rudolphine Tables 
he was able to use them to calculate when these transits 
would take place ; and he showed that both Mercury and 
Venus would cross the sun's disc on certain days in the 
year 163 1. A French philosopher named Gassendi took 
advantage of this prediction, and managed to observe Mer- 
cury passing across the face of the sun on November 7, 1 63 1. 
He was the first w T ho ever observed a transit With Venus 
he was not so fortunate, for the transit of that planet took 
place when it was night at Paris, and so Gassendi had no 
chance of observing it 

It was not long, however, before this too was seen. It 
must be remembered that two transits of Venus occur close 
together with only eight years between them. Now Kepler 
had imagined that in 1639 Venus would pass a little to the 
south of the sun, and so no transit would take place. A 
young Englishman, however, named Jeremiah Horrocks, 
only twenty years of age, after going carefully over Kepler's 
tables, felt convinced that there would be a transit, and he 
even calculated within a few minutes the time when Venus 
would enter upon the sun's face. Full of enthusiasm at the 
chance of seeing this grand sight, he wrote to a friend at a 
distance, begging him also to watch through the telescope at 
three o'clock on the afternoon of December 4, 1639, His 
expectations were not disappointed, for at fifteen minutes 
past three on that day the planet began to creep over the 
face of the sun. For twenty minutes Hnrrnr.ks watched it, 
and then the sun set and he could see no more. He had 
been able to notice, however, that Venus was much smaller 
in comparison with the sun than had been formerly supposed. 
Horrocks and his friend Crabtree were the only people in 



ch. xix. HALLEY' S METHOD. 155 

the whole world who saw this transit of Venus, the first one 
ever observed. 

1691. Halley suggests that the Sun's Distance may 
be measured by the Transit of Venus in 1761. — This was 
all that was known about transits when Halley went to St. 
Helena in 1676 to study the stars of the Southern Hemi- 
sphere. Here he also observed a transit of Mercury, and 
after watching the small black spot travelling across the face 
of the sun, and noting the time it took in going from one 
side to the other, the idea occurred to him that it would be 
possible to learn the distance of the sun by measuring the 
path of a planet across its face. As Mercury, however, is 
very far from us, and near to the sun, it would not answer 
the purpose so well as Venus, which is much nearer the 
earth. 

Halley knew that another transit of Venus would take 
place in 1761, and as he could not hope to live till then, he 
read a paper to the Royal Society in 1691, and another in 
17 16, beseeching the astronomers who should live after him 
not to let such an opportunity pass, and describing the way 
in which the observations should be made. It is this 
method which we must now try to understand as far as it is 
possible without mathematics. 

First of all I must mention two facts which astronomers 
knew already. The proportion of the distances of the 
planets was ascertained, as you will remember, by Kepler 
(see p. 98). Therefore it was known that Venus is (in 
round numbers) 2\ times as far from the sun as she is from 
the earth. It was also known by the apparent size of the 
sun that the sun's distance is about 108 times his diameter ; or, 
in other words, if you could measure the number of miles 
across the face of the sun and multiply that number by 108, 
it would give you the sun's distance from the earth. 



i 5 6 



SEVENTEENTH CENTURY. 




Therefore the one point to be learnt was, How many miles 
wide is the face of the sun ? 

Now suppose you place a globe or any other object upon 
the table in the middle of the room, as at g, Fig. 26, and 
«/ d c c place yourself at the 

point a. The globe will 
then hide from you (or 
eclipse) the point c on 
the opposite wall. Move 
your position to b, and 
the globe will then hide 
A d the point d. If the globe 

Diagram showing how the distance between the * S ( aS at G ) exactly half- 
points d c and d c can be known without way between you and the 

measuring them. ill 

G, A globe half-way between dc and a B. g, A wa U; the tWO points D 
globe three times as far from d c as from a b. an A r> will be the Same 

distance apart as the points a and b. But if you move the 
globe to g, which is three times as far from the opposite wall 
as it is from you, then the points d and c will also be three 
times as far apart as the points a and b. So that by know- 
ing how much farther the globe is from the wall than it is 
from you, you can tell accurately the distance between the 
points hidden without measuring them. 

It is exactly in this way that Halley proposed to measure 
off a certain number of miles upon the face of the sun. We 
are able to learn accurately how many miles distant any two 
places are upon our globe. Suppose, therefore, that two 
men go to places 7200 miles apart, and each observes 
Venus at a particular moment upon the sun's face. Just as 
you, from two different positions, saw the globe cover two 
different points of the wall, so these men will see Venus 
against different points in the sun, as in Fig. 2 7 ; and since 
the distance between Venus and the sun is i\ times her 



CH. XTX. 



THE SUN'S DIAMETER. 



157 



distance from the earth, the two points will be 2\ times 
7200 miles, that is 18,000 miles apart. Here, then, we 




Fig. 27. 
Venus as seen upon the sun by two observers, one at e' and one at e. (Proctor.) 
s, The sun. v v', Appearance of Venus on the sun's face. Venus is travelling in the 
direction of the arrow. 

have a certain number of miles measured off on the sun's face. 
But how are we to tell accurately what proportion this 
interval between the spots bears to the whole diameter of 
the sun? 

By Halley's method the whole time that Venus takes in 
crossing the sun is used as the means of measurement. 
The observer at each of the two stations notes exactly the 
time when Venus begins to 
cross the face of the sun, and 
the moment when she passes 
off it again, and so reckons 
exactly how long she has taken 
in making the whole transit. 

It was already known, from 
the rate at which Venus 
moves, exactly how long she 
would take in crossing the 
centre or widest part of the 
sun. We will call this time 6 
hours, so as to use whole num- 
bers. Now it is clear that in 
crossing a narrower part of 
the disc she will take less time 
one man says she was exactly 5 hours crossing from a to 
b, Fig. 28, and the other that she was 5^ hours crossing 




Fig. 28. 
Transit of Venus. 
Face of the sun. v, Venus. A B, 
Transit observed so as to occupy five 
hours, c d, Same transit observed so 
as to occupy five-and-a-quarter hours. 

Suppose, therefore, that 



158 SEVENTEENTH CENTURY. pt. ill. 

from c to D. This will give us the measurement neces- 
sary to lay down the position of the two transits on 
paper. 

Draw a circle any size you please, and, ruling a line 
across the centre, divide it into six parts (as in Fig 28 1 ), to 
represent the six hours which Venus would take in crossing 
the centre ; each of those parts will then represent the dis- 
tance which she travels in an hour ; 5^- of these, therefore, 
will be the distance she travels in 5J hours. Take this 
length in your compasses, and place it at any part of the 
circle where it will meet the edge at both ends, and in that 
position draw the line c D. Then take a second length of 
five parts only, and placing it below the other, rule the line 
a b parallel to c d. These two lines express the path of 
Venus, as observed by the two men, and we already know 
that the distance between them is 2\ times 7200, or 18,000 
miles. 

It is now easy to compare this interval with the sun's 
diameter. Suppose, for instance, that 47 such spaces will 
cover the whole diameter of the circle, as they would if the 
lines were drawn accurately in the observed positions, then 
18,000 x 47, or 846,000 miles, would be the measure of the 
sun's diameter. Now, we saw (p. 155) that the sun's dis- 
tance is 108 times his diameter; therefore 846,000 x 108, 
or 91,368,000 miles would, by these measurements, 
be the distance of the sun from the earth ; and this is as 
near as we can arrive at the truth when taking whole 
numbers. 

You will perhaps ask, if the measurement of the transit 
is such a simple process, why it 'takes months to make the 
proper calculations. But you must remember that in our 

1 It must be drawn very much, larger to approach to anything like 
qccuracy. This figure merely indicates the method. 



ch. xix. H ALLEY'S COMET. 159 

description we have neglected all the difficulties which really 
occur. Our earth is not standing still as we have supposed 
it to be. It is not only moving along in its orbit, but it is 
turning round on its axis all the time, and this has to be 
very carefully considered in choosing stations for observing 
the transit, and allowed for in the results. Then, since our 
earth moves in an ellipse, we are not always at the same 
distance from the sun ; this also has to be allowed for. 
Such simple difficulties as these you can understand, but 
there are a great number of others which make the calcula- 
tions very complicated indeed. Therefore you must not 
imagine that you know all about the transit of Venus when 
you have read this description of Halley's method. If you 
have some general idea of the way by which the sun's 
distance is found out, you will have learnt more than many 
people ; and you must wait till you have studied mathe- 
matics before you can expect to have a thorough knowledge 
of the matter. 

You will be glad to hear that Halley's advice was not 
neglected. Several transit expeditions were sent out in 1 7 6 1 , 
and again in 1 7 69, when the celebrated Captain Cook made a 
voyage to the Pacific Ocean for this purpose ; and it is to 
correct these observations that no less than forty-six expe- 
ditions were sent out in 1874 from Europe and America, 
and again in 1882 all nations sent observers to favourable 
spots. Now that these two transits are over, there will not 
be an other^ op portunity until De cember 200 7. Halley 
made many other valuable astronomical observations. He 
wa s the first astronomer who foretold the return of a comeJ u- 
Before his time it was thought that they went away and 
never came back again; but when the comet of 1682 
appeared, Halley began to search for former records of 
comets and found that one had been seen about every 



i6o SEVENTEENTH CENTURY. PT. ill. 

seventy-six years, reckoning backwards from 1682. There- 
fore he thought these must all be the same comet, and he 
foretold its return in 1758. It came as predicted, and 
has ever since been called ' Halley's comet' Halley 
died in 1742, and with him ends the astronomy of the 
seventeenth century. 

Besides the discoveries we have mentioned there was a 
great advance in the attention paid by government to the 
study of astronomy. In 1675 the celebrated observer 
Flamsteed was appointed astronomer to the King, and the 
' Royal Observatory ' at Greenwich, then called Flamsteed 
House, was built in order that regular observations might 
be carried on. Since 1675 there has always been an 
Astronomer-Royal in England. 



Chief Works consulted. — Proctor's ( Transits of "Venus ; ' HerschePs 
' Astronomy ; ' Denison's ' Astronomy without Mathematics ; J AirVs 
• Popular Astronomy.' 



ch. xx. THE DISPERSION OF LIGHT. 161 



CHAPTER XX. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Newton on Dispersion of Light — Chester More Hall — Dispersive 
Power in Flint and Crown Glass — Newton on the Transmission of 
Sound — Last years of Newton's life. 

Newton publishes his Discovery of the Dispersion of 
Light, 1671. — We must now return to Newton, and con- 
sider his third great discovery, which was about light. You 
will remember that he had to wait sixteen years between his 
first attempt to investigate the law of gravitation, and that 
new measurement of the earth which enabled him to prove 
the truth of his theory. During this time he had by no 
means been idle. He once said that the reason he had 
succeeded in making discoveries was that he gave all his 
attention to one subject at a time; from 1666 to 1671, 
when his papers on gravitation were quite laid aside, the 
subject to which he devoted himself was Light. 

In the early part of the seventeenth century several 
people had tried to find out what it was that gave rise to 
different colours. An Italian Archbishop named Antonio 
de Dominis (died 1625) had given a better explanation of 
the rainbow than Roger. Bacon had given before him ; and 
Descartes had gone farther, and had pointed out that a ray 
of light seen through a clear, polished piece of glass, cut into 
the shape of a prism (see Fig. 29), is spread out into colours | 



162 



SEVENTEENTH CENTURY. 



exactly like the rainbow ; but no one had yet been able to 
say what was the cajis g, of these different tints. Newt on 
was the first to work this out in his 
usual accurate and pamstaHng way. 

He tells us that in 1666 he 'pro- 
cured a triangular glass prism, to try 
therewith the celebrated phenomena of 
colours,' and in the very first experiment he was struck by a 
very curious fact. He had made a round hole f (Fig. 30), 




Fig. 29. 
Glass Prism. 




Fig 30. 

Newton's first Experiment on Dispersion of Light. 

D E, Window shutter, f, Round hole in it. A B c, Glass prism. M N, Wall on 

which the spectrum was thrown. 

about one-third of an inch broad, in the window-shutter, d e, 
of a dark room, and placed close to it a glass prism, a b c, so 
as to refract the sun-light upwards towards the opposite wall 
of the room, m n, making the line of colours (red, orange, 
yellow, green, blue, indigo, and violet), which Descartes had 
pointed out, and which Newton called a spectrum, from 
specto, I behold. 

While he was watching and admiring the beautiful 
colours, the thought struck him that it was curious the 
spectrum should be long instead of round. The rays of 
light come from the sun, which is • round, therefore if they 
were all bent or refracted equally, there ought to be a 
rowid spot upon the wall ; instead of which it was long 
with rounded ends, like a sun drawn out lengthways. What 



CH. xx. THE DISPERSION OF LIGHT. 163 

could be the reason of the rays falling into this long shape ? 
At first he thought that it might be because some of them 
passed through a thinner part of the prism, and so were less 
refracted ; but when he tested this by sending one ray through 
a thin part of the prism, and another through a thick part, 
he found that they were both equally spread out into a 
spectrum. Then he thought that there might be some flaw 
in the glass, and he took another prism ; still, however, the 
spectrum remained long, as before. Next he considered 
whether the different angles at which the rays of the sun fell 
upon the prism had anything to do with it, but after calcu- 
lating this mathematically he found the difference was too 
small to have any effect. Finally, he tried whether it was 
possible that the rays had been bent into curves in passing 
through the prism, but he found by measurement that this 
again was not the reason. 

At last, after carefully proving that none of these expla- 
nations was the true one, he began to suspect that it must 
be something peculiar in the different coloured rays them- 
selves which caused them to divide one from the other. 
To prove this he made the following experiment: — He made 
a hole f, in the shutter, as before, and passed the light 
through the prism, abc, throwing the spectrum upon a 
screen, m n. He then pierced a tiny hole through the screen 
at the point g, Fig. 3 1 ; the hole in this board was so small 
that the rays of only one colour could pass through at a 
time. Newton first let a red ray pass through, so that it was 
bent by the prism, h i k, on the other side of the screen, 
and made a shaded red spot on the wall, o p, at r ; here he 
put a mark. He now moved the first prism, a b c, a little, 
so as to let the second, or orange ray pass through the hole 
g. This ray fell upon exactly the same spot of the second 
prism, h 1 k, as the red ray had done, but it did not go to 



164 



SEVENTEENTH CENTURY. 



PT. III. 



the same spot on the wall ; it was more bent in passing 
through the prism, and made an orange spot at o, above the 
point r. By this Newton knew that an orange ray is more 
refracted in passing through a prism than a red ray is. He 
moved his prism, a b c, again, so as to let the yellow ray 




Fig. 31. 
Diagram showing the Different Refraction of Rays of Different Colours. 
D E, Shutter, f, Round hole. A b c, First prism, m n, Screen receiving the 
spectrum, g, Small hole through which the rays of only one colour can pass. 
h 1 k, Second prism refracting those rays, 

through. This was still more bent, and fell above o on the 
point v. In this way he let alt the different coloured rays 
pass through the hole, marking the points on which they 
fell, and he found that each ray was more bent than the last 
one, till he had marked out a second complete spectrum on 
the wall. Only the two extreme rays, red and violet, are 
traced out in Fig. 31, to avoid confusion. 
) This experiment proved clearly, 1 st, thatji^htjsjnadej/p 
of di fferently coloured_ jziys ; and 2d, th at these rays ai'e 
differe7itly refracted in passing through a pri sm. The red rays 
are least bent, and the violet ones most, while each of the 
other rays between these have their own course through the 
prism. I must warn you, however, not to think that there 
are exactly seven colours : there are really an infinite number, 
passing gradually into each other; Newton only divided them 
roughly into seven for convenience. 



ch. xx. NEWTON — DISPERSION OF LIGHT. 165 

This spreading out of the different coloured rays is called 
the dispersion of light. I wish I could give you the many 
beautiful experiments which Newton made to prove it, but 
we have only room for one, which you can easily try for 
yourself, by which the different colours which make up 
the spectrum can be turned back again into white light. 
You will see at once that if it is true that white light can 
be divided up into colours, those same colours when re- 
united must make white. To show this Newton took a 
round card and painted upon it the seven colours, as pure as 
possible, five times over, like a spectrum five times repeated 
(a, Fig. 32), and then spun it round rapidly, so that the eye 
received the impression of all the seven colours at once 
A 




Fig. 32. 
A, Newton's disc, b, Disc rotating. 

(b, Fig. 32). If you do this you will see the card looks a 
dirty white, because the colours blend together just as they 
do in a ray of light. You will not get a pure white, because 
the artificial colours are not pure, and also because it is 
difficult to paint each colour in the proper proportion. 

But now that we have proved that light is broken up 
into colours in passing through a denser medium, you may 
perhaps ask how it is that we do not see coloured rays when- 
ever we look at the sun through glass or any other trans- 



1 66 SEVENTEENTH CENTURY. pt. hi. 

parent substance. The reason is that when the two sides of 
the glass are parallel (that is, lie always at the same distance 
from each other), the ray of light is bent just as much in 
going out from the glass into the air as it was when it came 
in from the air into the glass, and so it remains just as it was 
at first. When the two sides are not parallel, as in a rounded 
lens, colours do appear in the thin edges of the glass, and 
these used to be very troublesome in telescopes and micro- 
scopes. Newton thought that they could never be got rid 
of, for he did not know that light is spread out or dispersed 
more in one kind of glass than in another. But two years 
after his death, in 1729, Mr. Chester More Hall, of Essex, 
found that two kinds of glass (flint-glass and crown-glass) 
disperse light differently, so that when you put them together 
they correct each other, and the coloured rays at the edges 
are blended into white light. Telescopes and microscopes 
which are made in this way are called achromatic (from a, 
without ; chroma, colour). A patent for such instruments was 
taken out by a Mr. Dollond in 1757, and he probably in- 
vented them without having heard of Mr. Hall's discovery. 

It would require a whole volume to give all Newton's 
investigations into the nature of light, and his experiments 
on the coloured rings of the soap-bubble and other trans- 
parent substances. His work on Optics was read before the 
Royal Society in 167 1 and 1672, but the ideas were so new 
that many clever men, who should have known better, 
attacked him with a number of foolish and ignorant ob- 
jections, till at last he told his friend Huyghens that he was 
almost sorry he had ever made them public. 

Newton explains how Sound is transmitted through 
the Air. — There is yet another branch of physics, in which 
we -owe much to Newton , namely, the study o f jsound. 
Pythagoras, Galileo, and Bacon had all taught that sound is 



ch. xx. NEWTON — TRANSMISSION OF SOUND. 167 

a vibration of the air which we feel when it acts upon the 
drum of our ear ; but none of these men had shown what 
kind of vibration this is. Newton was the first to suggest 
that it is caused by the particles of air moving backwards 
and forwards in the direction in which the sound travels ; 
the first particle being set in motion oy some impulse given 
to it, and thus striking the second ; the second striking the 
third ; and so on until the particle nearest the drum of our 
ear hits it, causing it also to oscillate backwards and for- 
wards, and producing in us the sensation of sound. 

Many persons find it difficult to understand how waves 
of sound can travel for long distances, while the air-particles 
forming the waves only move to and fro within very small 
spaces. One of the best ways to realise how this can be 
is to watch a railway train which has been bumped by a 
luggage van being joined on to it. The first push to the 
stationary train will have been given by the van, which 
bumping against the first carriage, will cause it to bump 
against the second ; this in its turn will bump against the 
third, and the movement will thus pass on to the end of 
the line, so that if you were standing there the last carriage 
would knock you down. Yet each carriage will at the 
most have only stirred a foot or two from its place, and in 
the end they may all settle down nearly in their original 
positions. If you are standing by the side of the train 
which is beingjslmrited, and watch it carefully, the reason 
of this will be clear. You will see that though the first car- 
riage drives on the second, and the second the third, yet 
before many carriages have been so driven, the first carriage 
will have rebounded, and be moving away from the second, 
which, in its turn, will move away from the third ; so that 
while the fourth, fifth, and sixth carriages are sending on 
the bump and are huddled together, 1, 2, and 3 are moving 



168 



SEVENTEENTH CENTURY. 



PT. III. 



backwards and apart; an instant later, 4, 5, and 6 will be 
drawing apart, in their turn, while 7, 8, and 9 will be close 
together, and so on to the end of the train. In this way a 
movement will pass along the whole line, every three or 
more carriages being huddled together, while the set behind 
them are separating, and this oscillation will go on until 
the train comes to rest. A movement exactly similar to 
this takes place in a wave of sound. The particles of air set 
in motion at one end are pushed forward, strike, and rebound 
just as the carriages do, and thus the movement is passed 
along the whole mass of air, while the particles themselves 
are oscillating backwards and forwards within very narrow 
limits. This movement, if visible, would have the appear- 
ance of Fig. 33 : a condensation or crowding of the particles 
a, and a rarefaction or separation of the particles b, occurring 



1! iiiii]| 1111 in 

111 1 1111111 1 ii urn mil 



Fig. 33. 
Waves of Sound, a, A condensation ; b, a rarefaction. From a to a, or b to b, is 
called a sound-wave, and varies in length according to the depth or shrillness of 
the sound. 

one after the other. The space from one condensation to 
another, or from one rarefaction to another, is called a wave 
of sound. 

In one way, however, sound travels somewhat differently 
to the wave of movement along a train. The carriages of 
a train are confined in one straight line, just as air particles 
would be if they moved in a tube ; but in the open air the 
particles can move in all directions, and therefore sound 
does not only travel in one straight line, but spreads out in 
all directions in expanding spheres, unless it meets with some 



CH. xx. NEWTON— TRANSMISSION OF SOUND. 169 

obstacle by which the movement is driven back, and then 
the sound is reflected. Newton not only pointed out how 
sound travels, he also attempted to ascertain at what rate 
it travels, and he showed that the more elastic and less 
dense air is, the more rapidly it will convey sound. A very 
elastic substance, in the proper sense of the word, is one 
which will spring back to its original shape whenever it is 
set free, just as a steel spring does. Now in the case of 
the train, if it happen to be composed of a set of heavy 
trucks with no springs between them, they will move slug- 
gishly, and the waves of compression and rarefaction will 
take place but slowly. But if the train be composed of 
light carriages with springs at the end of the buffers, then 
each carriage will rebound much more quickly, both be- 
cause it is lighter, and because the elasticity of the springs 
will help the rebound Now when air is heated, if it can- 
not expand it becomes more elastic, and if it can expand 
it becomes lighter than when it is colder, and therefore in 
either case sound will travel more quickly along warm air 
than along cold. 

Newton tried to calculate the rate at which sound travels, 
but he did not know that the mere fact of the sound- 
wave passing along makes the air hotter and therefore more 
elastic, so his results were not strictly accurate. We know 
now that in air which has a temperature of 32 Fahr., 
sound travels at the rate of 1090 feet per second, while in 
air of the ordinary temperature of 52 Fahr., it travels at the 
rate of 1 1 1 2 feet per second. 

Newton's account of his experiments on sound are 
to be found in the second Book of his ' Principia.' After 
this great work was published, in 1687, he next turned 
his attention to chemistry, but unfortunately all the re- 
sults of his labour in this science were destroyed by an 



170 SEVENTEENTH CENTURY. pt. iil 

accident. One day when he was in chapel his pet dog 
Diamond turned over a lighted taper, which set fire to all 
the papers on which his work was written. When he re- 
turned and found the charred heap it is said that he merely 
exclaimed, ' O Diamond, Diamond ! thou little thinkest 
the mischief thou hast done ! ' but his grief at the loss of 
his work affected his brain, and though he recovered and 
lived another forty years, publishing many editions of his 
works, yet he never made any more great discoveries. 

Newton received many honours in his old age : in 1699 
he was appointed Master of the Mint, and a member of the 
French Royal Academy of Sciences ; in 1703 he was made 
President of the Royal Society, and in 1705 he was knighted 
by Queen Anne. Like all truly great men, he was modest 
as to his own abilities, and always willing to be taught by 
others. He felt so strongly how much we have still to 
learn about the Universe, that he considered his own dis- 
coveries as very trifling indeed. A short time before his 
death he said of himself, ' I know not what the world may 
think of my labours ; but to myself I seem to have been only 
like a boy playing on the sea-shore, and diverting myself in 
now and then finding a smoother pebble or a prettier shell 
than ordinary, whilst the great ocean of truth lay all un- 
discovered before me.' Yet this man who spoke so humbly 
was the discoverer of the greatest and most universal law 
known to mankind ! He loved to seek out new laws, but he 
was more anxious to collect facts and to make sure that he 
was right, than eager to publish his conclusions. It was the 
truth he loved, and not the fame which it brought. His 
patience and perseverance were unbounded ; he was never 
in a hurry, but turned a subject over and over in his mind 
for years together, seizing upon every new light shed upon 
it, and waiting patiently for more. And through all his 



ch. xx. DEATH OF NEWTON. 171 

labours he looked reverently up to the One Great Light 
whose guiding power he loved to trace and to acknowledge 
in all the wonders of the universe. He died in 1727 at 
eighty-five years of age, and was buried in Westminster 
Abbey, his pall being borne by the first nobles of the land. 



Chief Works consisted. — Newton's 'Optics,' 172 1 ; Ganot's 
' Physics ; ' Rossiter's ' Physics ; ' Brewster's ' Encyclopaedia/ art. 
' Optics ; ' Herschel's ' Familiar Lectures j ' Newton's ' Principia,' 
Book 11. ; Brewster's ' Life of Newton.' 



172 SEVENTEENTH CENTURY. pt. in. 



CHAPTER XXI. 

SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 

Roemer — Velocity of Light — Huyghens — Cycloidal Pendulum — Cor- 
puscular and Undulatory Theories of Light — Refraction — Double 
Refraction. 

Olaus Roemer measures the Velocity of Light, 1676. 

— While Newton was dispersing light in prisms, and finding 
out its nature, Olaus Roemer, a famous Danish astronomer 
(born 1644, died 17 10), was engaged in something almost 
as wonderful He was measuring the rate at which light 
travels across the sky ! It seems at first as if this would 
be impossible, but we now know three different ways of 
accomplishing it ; Roemer's was the first attempt ever made, 
and his measurement was very near indeed to the truth. 

You will remember that Jupiter has four moons, which 
move round it as our moon moves round our earth. Three 
of these moons are so near to Jupiter, and move round it in 
such a manner, that they pass through its shadow and are 
eclipsed every time they go round. Now it became very 
useful, for certain astronomical reasons, to know exactly when 
these eclipses happened, and the time of their occurrence 
was therefore calculated very carefully ever since Galileo 
first discovered them. There was no difficulty in doing this, 
and yet, strange to say, the eclipses rarely happened exactly 
at the right moment. Sometimes they were too early, some- 



ch. xxr. VELOCITY OF LIGHT. 173 

times too late ; and they varied, according to some regular 
rule, as much as 16 minutes 36 seconds on each side of the 
exact moment when they ought to have happened. 

At last it occurred to Roemer, and to an Italian astrono- 
mer named Cassini, that, as Jupiter is farther away from the 
earth at one time than another, the e clipse s might be seen 
some minu tes late r whenever the rays of light from the 
moons had to cross a greater distance t6~~reach the earth. 
Cassini seems tohave put the thought aside and not to have 
worked it out ; but Roemer seized upon it, and by careful 
calculations proved that it was the true answer to the diffi- 
culty. If the earth was at e (Fig. 34) for example, when 




Fig. 34. 

Different Distances at which Jupiter's Light reaches the Earth. 

j, Jupiter, e e', The Earth. 

Jupiter was at j, the light would not have nearly so far to 
travel as if the earth was at e'; and in this last position the 
16 minutes 36 seconds would be taken up by the light 
crossing the earth's orbit from e to e'. This distance was 
known to be about 190,000,000 miles, so that light travels at 
the rate of 190,000,000 miles in 996 seconds, or about 
190,000 miles in a second. This is nine million times as 
fast as the quickest express train. 

Huyghens and Newton— Theories of Light. — The 
time had now come when so much was known about the way 
in which light behaves, that philosophers began to ask them- 
selves, 'What is Light?' — a question by no means so easily 
answered as you may think ; for though it is by means of 



174 SEVENTEENTH CENTURY. pt. iil 

light that we see even-thing, yet light in itself is invisible. 
You will exclaim at onpe that you can see a sunbeam 
shining through a crack in a window-shutter. But what you 
see is not light itself, it is the particles of dust or smoke 
which reflect the light so that they shine. There is one 
very simple way of proving to yourself that rays of light are 
not visible lines. When the moon is shining you know that 
it is reflecting the light of the sun, therefore there must be 
light crossing the sky and falling upon the surface of the 
moon. But now look up some other night when the moon 
is not there. All is darkness ; yet the light must be there 
just the same, and would have caused the moon to shine 
if it had been there also, but as there is nothing to reflect 
it to your eye it is invisible. 

What, then, is this light, invisible in itself, yet without 
which we can see nothing? Newton thought that it was 
composed of minute invisible particles of matter which darted 
out in straight lines from luminous or light-giving bodies, 
and falling upon our eyes caused the sensation which we 
call light. This is called the Corpuscular, or sometimes the 
£??iission, Theory of Light. It was very ingenious, and 
accounted for a great many of the facts, but there were 
many others which it did not explain ; and I will not 
attempt to describe it to you, because another theory, called 
the Undulator^ (or wave) Theory of Light, has now been 
found to be much more complete and satisfactory. This 
last theory was proposed by a Dutch mathematician and 
astronomer named Christian Hugghens 3 the son of Constan- 
tine Huyghens, Counsellor to the Prince of Orange. 

Christian Huyghens was born at the Hague, in Holland, 
in the year 1629; when he was only thirteen years old he 
was already passionately fond of mathematics, and ex- 
amined every piece of machinery that fell in his way. He 



ch. xxi. VARIOUS THEORIES OF LIGHT. 175 

received a very good education, and wrote some able treatises 
upon geometry when he was only two-and-twenty. From 
this time he advanced very rapidly, both writing valuable 
papers and making grand discoveries. In 1658 he invented 
a peculiar kind of pendulum called the cycloidal p endulum, 
which would keep accurate time when swinging over wide 
spaces ; and he was also the first to apply pendulums t o 
clocks. In 1659 he made a telescope ten feet long, with 
which he discovered one of Saturn's satellit es, and descri bed 
a ccurately Saturn's rin g, which Galileo had mistaken for two 
stars. In 1660 he came to England and solved some 
questions which the Royal Society had proposed about 
the laws of motion. Then he was invited to settle in France, 
and it was there, in 1678, that he read before the ' Academie 
des Sciences ' the theory of light which we must now try to 
understand. 

Undulatory Theory of Light, 1678. — We have seen 
that it had been known ever since the time of the Greeks, 
that sound is caused by a trembling or vibration of the air, 
so that when you strike the wire of a harp, the trembling of 
the string shakes the air, and the quivering motion travels 
along until some wave strikes the drum of your ear and pro- 
duces the sensation we call sound. 

Now Huyghens said, ' We can only explain light by sup- 
posing it to be a vibration like sound.' But here at the 
very outset came a difficulty. We know that light is not a 
vibration of the air, for if you draw the air completely out ol 
a glass vessel, light will still pass across it ; and besides, we 
get light from the sun and the distant stars, so that it has to 
come across a great airless space before it reaches the at- 
mosphere of our earth. And yet, if light is a vibration, it is 
clear there must be something between the sun and us to 
vibrate. To meet this difficulty Huyghens supposed the 



1 76 SEVENTEENTH CENTURY. PT. in. 

whole of space between our earth and the most distant stars to 
be filled with an elastic invisible substance which he called 
1 ether.' He assumed this substance to be so fine and 
subtle that it passes between the atoms, even of solid 
objects, and that the sun and all luminous bodies cause it 
to vibrate so that its undulations or waves strike upon our 
eyes and give rise to the sensation we call light. 

Thus, according to this theory, when you look at the 
sun, the invisible 'ether' filling the whole space between 
you and it, is moving up and down in rapid vibrations, just; 
as if the sun held one end of a cloth and you the other, and 
the sun was shaking the cloth so that the waves traveller 1 
along it to your eye ; and every wave that hit yoi- would 
cause the sensation called light 

This theory explains very well how light-waves may be 
in the sky and yet we may not see them ; for if a stick 
is moving rapidly to and fro in the air, and you go within 
reach of it you feel pain, but if you keep out of reach no 
pain is produced. In the same way, when the vibration of 
this invisible ether strikes your eye you feel light, but 
though the waves may be travelling rapidly across the sky, 
so long as they do not fall upon your eye, no light will be 
produced to you. 

But suppose you were not looking at the sun, but at the 
ground, why should you still see ? Because the waves from 
the sun which strike the ground cannot travel on so easily 
through the solid earth as through the pure ether, so a great 
number of them bound off and vibrate back along the ether 
again, from the ground to your eye ; and as they vibrate dif- 
ferently according as the ground is rough or smooth, hard or 
soft, wet or dry, they make a different impression upon your 
eye, and cause you to see a picture of the ground as it is. 

Clear white glass and other perfectly transparent bodies 



ch. xxi. THE UNDULATORY THEORY. 177 

— - — 

allow nearly all the waves of light to pass through them and 
send hardly any back to your eye ; and people have in con- 
sequence been known to walk right up against glass doors 
without seeing them. Bright polished surfaces, on the con- 
trary, like steel and mercury, turn nearly all the waves back 
again, and this is why we see our own faces reflected so clearly 
in a looking-glass, where it is the mercury at the back which 
is the real mirror. 

If we had room we might follow out these light-vibrations 
in a very interesting manner. For instance, why does a 
leaf look green and a soldier's coat red ? Because, as in 
sound the kind of note you hear depends upon the quick- 
ness of the vibrations of the air, so in light it depends upon 
the quickness of the vibrations of the ether what colour you 
see. The vibrations which produce violet, indigo, blue, 
green, yellow, orange, and red, have travelled all together as 
white light through the ether, but they are differently treated 
by the leaf. All except the green waves are quenched, or 
absorbed as it is called, by the material of the leaf, and only 
the green waves bound back upon your eye. In other words, 
the vibrations of the ether coming from the leaf move ex- 
actly fast enough to produce upon your eye the sensation 
you call green, just as the vibration of the air caused by a 
particular string of a harp produces on your ear the sensa- 
tion of the note you call the middle C. 

Refraction of Light explained by Huyghens. — But 
we must now go back to Huyghens, and point out how beauti- 
fully he explained by his undulatory theory the refraction or 
bending-back of rays of which we have already spoken so 
much. When a wave of light is travelling onwards, he said, 
if it passes vertically into glass or any denser substance, the 
wave will move more slowly, but it will still go straight on, 
because both ends of the wave will be equally checked. 



178 



SEVENTEENTH CENTURY. 



PT. III. 



But if the wave goes into the glass obliquely (see p. 47), or 
into a glass with a rounded edge, one end of it will reach the 
glass first before the other, and will move slowly, while the 
other end goes on unchecked, and so the wave will swing 
round and will have its direction altered. In the same way, 
when it passes out again from the glass, one end will pass 
out first, and will move more easily in the air than the end 
that is still in the glass, and so it will swing round again 
and make another bend. 

This is somewhat difficult to understand at first sight, 
and it will be best explained by a very ingenious experiment 
proposed by Mr. E. B. Tylor. 1 Take two small wheels about 



vN 



^ ^ 



^ 




Fig. 35. 
Figures illustrating the passage of the waves of light through different- 
shaped lenses (Tylor). 

2 inches round, and mount them loosely upon a stout iron 
axle measuring about half-an-inch round. This will make a 
runner like two wheels of a cart, and if you let it roll down 
a smooth board it will represent very fairly the crests or tops 
of the waves of light in the ether. Let your board be about 
2 J feet long, and at one end of it glue on pieces of thick- 
piled velvet of the shape of lenses (see 1, 2, 3, Fig. 35). 
Let your runner first go straight down the board upon the 
oblong velvet, it will then run through the velvet without 
changing its course, as a vertical ray does through a lens. 
Then start it obliquely, as at a, across the board, so that it 

1 'Nature,' vol. ix. 1 874, p. 158. 



ch. xxi. DOUBLE REFRACTION OF LIGHT. 179 

will reach the velvet in the position b. Here the left wheel 
of the runner will touch the velvet first, and will be checked 
by the rough pile, while the right wheel moves on quickly 
as before, and thus the runner will swing round or be refracted 
into the direction b c. Then, as it passes out again, the 
left wheel will come out of the velvet first and will move 
more quickly on the smooth board, while the right is still 
checked by the velvet ; therefore the runner will again be 
shifted round or refracted as it passes out into the direction c d. 
In figure 2, on the other hand, even if the runner passes in 
vertically, yet the rounded surface of the lens causes the left 
wheel to enter first, and as, in consequence of the rounding 
of the second surface this same wheel comes out last, the ray 
is refracted inwards along its whole course. You can easily 
follow the course of the runner through the other lens for 
yourself, always noticing that the arrow marks which way the 
ray of light is coming ; and when you have done this you 
will have a beautiful imitation of the way in which the waves 
of light are refracted in passing from one medium to another. 
Double Refraction.— There is another remarkable fact 
about light which Huyghens explained ; namely, the double 
refraction of light through a crystal called Iceland spar. A 
physician of Copenhagen named Erasmus Bartholinus had 
received from Iceland a crystal in the form of a rhomboid 
(see Fig. 36), which, when broken, fell 
into pieces of the same shape. Bartho- 
linus called this crystal ' Iceland spar,' 
and while making experiments with it FlG . s6# 

he observed that an inkspot or any small a spot of ink seen through 

Object Seen through it appeared tO be a crystal of Iceland spar. 

doubled. He was not able to explain this curious fact, but he 
published an account of it in 1669, and Huyghens accounted 
for it quite correctly by suggesting that the crystal was more 



ED 



180 SEVENTEENTH CENTURY. pt. iil 

elastic in one direction than in the other, so that a wave of 
light passing into it was divided into two waves moving at 
different rates through the crystals. This would cause 
them to be bent differently — one according to the ordinary 
law of refraction (see p. 105), and the other in an extra- 
ordinary way. Thus these two separate rays entering the 
eye would cause there the impression of two objects. 
( This curious effect is very interesting to study, and it led 
Huyghens to make a number of remarkable experiments. 
He found that the two rays when they passed out at the 
other side of the crystal remained quite separate the one 
J from the other, and if they were afterwards sent through 
another crystal in the same direction that they had gone 
through the first, they went on each their own way. But 
now came a very extraordinary fact : if the second crystal 
was turned round a little so that the rays passed in rather a 
different direction through it, each ray was again split up 
into two, so that there were now four rays, sometimes all 
equally bright, sometimes of unequal brightness, but the 
light of all four was never greater than the light of the one 
ray, out of which they had all come. These four rays con- 
tinued apart while he turned the second crystal more and 
more round ; till, when he had turned it 90 , or a quarter 
of a circle, the rays became two again, with this remarkable 
peculiarity, that they had changed characters ! The ray 
which before had been refracted in the ordinary way now 
took the extraordinary direction, while the other chose the 
-ordinary one. 
/ This curious effect observed by Huyghens is now known 
/ as the 'polarisation of light' by crystals. There is a beauti- 
• ful explanation of it, but we must wait for that till we consider 
the science of the nineteenth century, for it is now much 
better understood Huyghens' ' Theory of Light ' was pub- 



ch. xxi. POLARISATION OF LIGHT. 181 

lished in 1690, under the title 'Traite de la Lumiere.' He 
remained in Paris for some years ; but left and returned to 
Holland when the persecution of the Protestants began after 
the revocation of the Edict of Nantes. He died in 1695. 



Chief Works consulted. — Herschel's 'Familiar Lectures' — art. 
'Light;' Tylor, 'On Refraction'— ' Nature,' vol. ix. ; « Edin. Phil. 
Journal,' vols. ii. and iii. — 'On Double Refraction;' Ganot's 'Phy- 
sics;' Encyclopaedias — ' Britannica,' ' Metropolitan, ' and Brewster's. 



182 SEVENTEENTH CENTURY. pt. iil 



CHAPTER XXII. 

SUMMARY OF THE SCIENCE OF THE SEVENTEENTH 
CENTURY. 

We have now arrived at the close of the seventeenth century, 
and it only remains for us, before going further, to try and 
picture to ourselves the great steps in advance which had 
been made between the years 1600 and 1700. We saw at 
p. 80 that the work of the sixteenth century consisted chiefly 
in making men aware of their own ignorance, and teaching 
them to inquire into the facts of nature, instead of merely 
repeating what they had heard from others. In the seven- 
teenth century we find them following out this rule of patient 
research, and being rewarded by arriving at grand and true 
laws. 

Astronomy.— To begin with Astronomy. Here Galileo 
led the way with his telescope. The structure of the moon, 
with its mountains and valleys ; the existence of Jupiter's 
four moons revolving round it and giving it light by night ; 
the myriads of stars of the Milky Way ; the spots of the sun 
coming into view at regular intervals, and thus proving that 
the sun turns on its axis ; all these discoveries forced upon 
men's minds the truth that our little world is not the centre 
of everything, but a mere speck among the millions of 
heavenly bodies. But while they humbled man's false pride 
in his own importance, they taught him, on the other hand, 
the true greatness which God has put in his power by giving 



ch. xxii. SUMMARY. 183 

him the intellect to discover and understand these wonderful 
truths if he will only seek them in an earnest and teachable 
spirit. 

Then came Kepler with a still grander lesson, for he 
showed that the movements of the planets are governed by 
regular and fixed laws, which can be traced out so accurately 
that an astronomer is able to foretell with confidence what 
will happen many years after he himself has passed away. 
Thus we see Gassendi and Horrocks, by the use of Kepler's 
labours, calculating within a few minutes the time of a 
planet's passage across the face of the sun and watching the 
exact fulfilment of the prediction. Nor is this all : so exact 
and true are these movements, and so completely is man 
able to read them rightly, that by this simple passage of a 
small black spot across the sun Halley showed that we may 
actually number the millions of miles between ourselves and 
the great light around which we move. We might almost 
think that we had now travelled as far as man's mind could 
go, but something far greater remained behind. Newton 
sitting under his apple-tree and pondering on the wonderful 
mechanism of the heavens, found the one great law which 
accounts for the movements of all the bodies in the universe 
— a law which explains equally why a pin falls to the ground 
and why a comet which has been lost to sight for more 
than seventy years will return to a certain fixed spot at a 
day and an hour which can be accurately foretold. Kepler 
had pointed out fixed and definite laws by which the uni- 
verse is governed ; Newton demonstrated that one law ex- 
plains them all. He showed us how one single thought, as 
it were, of the Divine mind suffices to govern the most 
complicated as well as the simplest movements of our 
system. 

All this advance from Galileo to Newton was the work 



1 84 SEVENTEENTH CENTURY. pt. in. 

of the seventeenth century. It began, you see, with certain 
simple facts ; by Galileo seeing that bodies existed in the 
heavens which were not known to be there before ; it ended 
in the beautiful lav/ of which we have just spoken. But I 
want you particularly to notice that this end would never 
have been reached by men who were content to sit d own 
idly and ta lk of t he greatne ss of God . It was the result of 
real work by men wh o tried fi rst to learn jhe facts, and from 
these to prove reverently the way in whic h it ple ases God to 
bring the m abo ut ; and in this labour of love, being brought 
face to face with the infinite grandeur of nature, they learnt 
that true humility which led Newton, the greatest of them 
all, to feel that he was but as a little child gathering pebbles 
on the shore of the great ocean of truth. 

Physics. — If we now turn to Physics, we shall find that 
the way to knowledge lay still along the same road of patient 
inquiry. Torricelli's barometer and Guericke's hemispheres 
of Magdeburg both proved by direct experiment that the 
atmosphere round our earth is pressing in all directions 
equally with great force ; and this again brings us round to 
the force of gravity, which is the cause of this pressure ; 
while Boyle's experiment showed that air is elastic, being 
compressed in exact proportion as the weight upon it is 
increased, and expanding again directly it is diminished. 
Newton showed that this elasticity of air gives rise to the 
waves of condensation and rarefaction, which convey an 
original impulse across wide spaces and produce the effect 
of sound upon our ears. 

Again, in the subject of Light, we begin with hard dry 
facts, which doubtless you may have thought it wearisome to 
master, but we end with a theory so wonderful and beautiful 
that it seems more like a fairy-tale than sober science. The 
first step here was the invention of the telescope, which. 



ch. xxii. SUMMARY. 185 



while it opened the road on the one hand to astronomical 
discoveries, also led to the grinding of lenses, and to a more 
careful study of the laws of light. This it was which caused 
Snellius to make experiments on the bending of rays with a 
view to improving telescopes, and so to discover the law of 
refraction, afterwards more fully stated by Descartes. Then 
we find this last philosopher trying to explain the rainbow, 
and studying the colours falling through a prism, and so the 
subject passed on into the hands of Newton. 

Here, by experiment again, the threads of light were dis- 
entangled in the prism, and Newton drew out its many- 
coloured rays, tracing them one by one on their road, till he 
had shown how they can be explained by dispersion, and that 
to this law, which seemed so uninteresting at first, we owe 
all the lovely colours which surround us. And now Huy- 
ghens takes up the story and leads us fairly into the invisible 
world. This light, which Roemer had proved to be travel- 
ling across space with marvellous speed, Huyghens shows 
to be no actual substance at all, but most probably a 
trembling of an invisible and intangible ether — a succession 
of infinitely tiny waves chasing each other across millions of 
miles, and striking at last on the minute opening of our eye, 
bringing to us the wonderful effects of light. As Newton 
traced colours, so Huyghens traces the invisible waves through 
many substances, showing us their path and why they take 
it ; and landing us at last in the bewildering effects of polar- 
isation, leaves us there to wait for more knowledge in a 
future century. 

Biology. — And now we come to Biology, or the study of 
all those sciences which relate to life. Here you must re- 
member that our account of the discoveries made must be 
more than usually imperfect, because the subject is more than 
usually difficult. Yet we can form some idea of the new 



186 SEVENTEENTH CENTURY. pt. hi. 

light thrown upon the nature of the living body, by Haryey's 
t heory of the c irc ulation of the blood and the discoveries 
which followed concerning the way in which nourishment is 
carried to it. We can see how Mayow's experiments, 
proving that part of the air is burnt within us. supplying heat 
to our bodies, would have been a grand step in advance if 
he had lived to make them more known, and how, indeed, 
they did influence those who came after, though his name 
was for a time forgotten. More clearly still we can under- 
stand ho w Malpighi's_and Grew's inves ti gations wit h the 
microscope, bringing to light hidden parts and vessels of the 
human frame, gave rise to a totally new branch of science, 
and enabled men to study the organisation of their own 

(bodies with an accuracy quite impossible before ; while the 
same method applied to Botany gave the first real insight into 
the structure of plants, tracing out their delicate organs, and 
even the tiny cells of which their flesh is composed. And 

< lastly, in the field of Natural History, w T e find that Ray and 
Willughby performed the immense task of classifying the 
whole animal and vegetable kingdoms, and laid the founda- 
tion of the grand generalisations of Linnaeus in the next 
century. 



SCIENCE OF THE 
EIGHTEENTH CENTURY. 



10 



Chief Men of Science in the Eighteenth Century. 



Boerhaj^e 
Hales . 
Halkr . 
Huntex. 
Bonnet . 
Spal lanzani . 
Buffon . 
Linnaeus 
Jussieu . 

Lazzaro Moro 
Werner 
Huttofl 
William Smith 

Black . 

Bergmann 

CavepH i^ 

Priestley 

Scheele 

Rutherford 

Lavois ier 

Sauveur 
Bernoulli 
Euler . 
Chladeic 




Bradley 

Maskelyne 

Lagrange 

Laplace 

Herschel 



A.D. 

1668-1738 
1677-1761 
1708-1777 
1 728- 1 793 
1720-1793 
1729-1799 
1707-1788 
1707-1778 
1699-1777 

1687 — 
1750-1817 
1726-1797 
1769-1839 

1728-1792 
1735-1784 
1731-1810 
1733-1804 
1742-1786 
1749-1819 
1743-1794 

1653 1716 
1700-1782 
1 707-1 783 
1756-1827 

1736-1819 
1706-1790 
1737-1798 
1745-1827 

1690-1762 
1732-1811 
1736-1813 
1749-1827 
1738-1822 



ch. xxiii. BE VELOPMENT OF SCIh VCE. 189 



CHAPTER XXIII. 

SCIENCE OF THE EIGHTEENTH CENTURY. 

Great spread of Science in the Eighteenth Century — Foundation of 
Leyden University in 1574 — Boerhaave, 1701 — Organic Chemistry 
— Dr. Hales' Experiments on Plants — Great Popularity of Boer- 
haave's Chemical Lectures. 

We have now arrived at the beginning of the eighteenth 
century, only 179 years before our own day, when the dif- 
ferent sciences which we have been tracing in their rise, like 
little rills on the mountain sides, were beginning to swell 
out into mighty streams, widening and spreading so rapidly 
that it is in vain we strain our eyes to try and watch 
them all The time had now come when any man who 
wished to be a discoverer was obliged to devote his whole 
life to one branch of science, following it out in all its in- 
tricate windings. And so we find that about this time each 
science begins to have a complete history of its own, with 
its own eminent men, and its peculiar language growing 
more and more technical, so as scarcely to be understood by 
ordinary readers. 

For this reason most general histories of Science stop at 
this point and refer their readers to special works on the 
different sciences. I do not, however, propose to do this ; 
for though, owing to the great strides which were being 
made, it will be impossible to give more than a few glimpses 
of the work that was being done, still I think that if we 






^ 



w 

>> 



190 EIGHTEENTH CENTURY. ft. hi. 

struggle on through the increasing mass of knowledge and 
gather up a fragment here and there, a general idea of the 
progress of science may be gained such as will enable young 
readers to turn to more advanced scientific books with much 
greater interest, even though they may learn very little of 
any one science. 

Astronomy, Physics, and to a certain extent Chemistry, 

had made such a start at the end of the seventeenth century 

that it was a great many years before those men who came 

after Newton, Halley, Huyghens, and Stahl, had mastered 

the new discoveries sufficiently to progress any farther. 

Therefore we find that it was not in these sciences that most 

* \ ^Ma&vance was made in the beginning of the eighteenth cen- 

^1/^ tury, but in those which relate to living beings, and which 

are all included under the head of Biology, or the science of 

life. Medicin e, Anatom y, and Ph ysiology were the branches 

which grew most rapidly about this time ; and the five great 

v M$° men whose names stand out most conspicuously are Boer- 

\**£f\ m4*~ haave, Hajl er, JojmJEiiniter, Bonnet, and Spailanzani: Boer- 

£<r^v^v , ^haaye as the founder of the "study of organic 'chemistry, 

& < \t\ / y JjJ ^ rQaller and Hunt er as the fathers of comparative anatomy, 

^s . ^ ^and Bon net and _Spallanzajii v as the discoverers of some very 

OJlW^ IA| remarkable facts m physiology} We will take these subjects 

^ V^X^r i n regular order, and try to understand something of the 

$r-r work which was done in them. 

S Medical School of Ley-den. — Foundation of Organic 

Chemistry by Boerhaave, 1701. — On the coast of Holland, 
just where the Rhine empties itself by a number of small 
channels into the German ocean, stands the city of Leyden, 
which became famous in the year 1574, on account of a 
siege of four months which the starving inhabitants endured 
with the utmost heroism, when the Protestant Netherlanders 
were struggling for life and liberty against Philip II. of Spain. 



ch, xxiir. HERMANN BOERHAAVE. igi 

The Dutchmen were successful at last, and drove out the 
Spanish army, by cutting away the dykes and letting in the 
sea to swallow up their beautiful pastures, their neat villages, 
and their fruitful orchards ; and as a reward for their de- 
votion to the cause, William of Orange founded the 
University of Leyden, which afterwards became very cele- 
brated. 

Hermann Boerhaave, of whose work we are now going 
to speak, was a Professor of Medicine in this University 
about a hundred years after its commencement. The son 
of a Dutch clergyman, he was born in 1668 at Vorhout, one 
of those same small Dutch villages near Leyden which had 
been for days under the sea in 1574. His father intended 
him for the church ; but the young student, having been 
accused of holding false opinions, was only too glad of this 
excuse to give up theology and study medicine, in which he 
delighted. He was so successful that in 1701 he was made 
Lecturer of Medicine in the University, and a few years 
later the Professorships of Chemistry and Botany were 
also given to him. From that time the Medical School of 
Leyden became famous all over the world. Students 
flocked to it from all quarters, and most of the best med- 
ical men of Europe were pupils of Boerhaave. This was 
due chiefly, of course, to his wonderful medical knowledge 
and his skill as a lecturer ; but his popularity was greatly 
increased by his enthusiasm, kindly temper, and the great 
interest which he took in the success of his pupils. He 
was always ready to help others and to give them credit 
for the work they had done, and it is said that even his 
enemies could not resist his constant and uniform kind- 
ness and good-temper. He loved his science too well to 
hinder its progress by angry disputes ; and by imparting 
this spirit to his pupils he did almost as much for the 



192 EIGHTEENTH CENTURY. pt. in. 



spread of medical science as by the facts which he taught 
them. 

But besides his influence upon medicine in general there 
was one particular study which Boerhaave may be said to 
have founded; namely that of organic chemistry, or the 
chemical analysis of substances occurring in plants and 
animals. You will remember that the false science of 
alchemy had always been much mixed up with chemistry, 
and the alchemists had some strange mystical notions about 
* vital fluids,' which they supposed to exist in animals and 
plants, and to cause their life and growth. Little by little, 
however, more correct ideas had grown up in the sixteenth 
and seventeenth centuries about the nature of life. Vesalius, 
Harvey, Malpighi, Grew, and many others, had gradually des- 
cribed more and more accurately the working of the different 
organs of a living being, and now Boerhaave went farther, 
and tried to discover by means of chemistry of what 
materials these organs themselves are composed. 

In the same way that Geber had decomposed or divided 
up inorganic substances, such as metals and earths, by distil- 
lation and sublimation (see p. 43), so Boerhaave proposed to 
decompose the ojganic structures of plants and animals, 
and to discover the materials contained in them. To 
accomplish this he took a plant, such as rosemary, and 
putting fresh moist leaves of it into a furnace, heated them 
gently and drove out all the moisture, which he collected 
in a separate vessel. When this moisture had cooled down 
into a liquid he examined it and found that it was made 
up of water, and of different kinds of oils and essences, 
according to the plant he had taken. For instance, from 
rosemary he got an essence with the peculiar scent of 
rosemary; from the bark of the cinnamon tree, Laurus 
Camphorum, or Cinnamomum camphorutn, he got essence of 



CH. xxiii. ORGANIC CHEMISTRY. 193 

cinnamon ; from its roots, camphor ; and from its leaves an 
oil with the taste of cloves. Then after he had extracted 
all the juice from the plant, he burnt the dry remains, to see 
what would be contained in its ashes after the fire had 
driven off part of the solid matter as gas, and he found in 
them a kind of salt, which was also different in different 
plants. But if he poured hot water on the plant before 
burning it, he found no salt in the ashes, for it had been 
dissolved and carried off in the water. 

Having now found of what materials the plant was com- 
posed, the next step was to discover where they came from ; 
so he took several specimens of earth in which plants can 
grow and examined them also ; and he found that he could 
extract from them many of the substances, such as salt, 
alum, borax, and sulphur, which he had also discovered in 
the ashes of the plants. It was clear, then, that the plant 
took these salts out of the earth ; and by a number of experi- 
ments he went on to prove that they are dissolved by the 
rain-water which sinks into the earth, and are then sucked 
up by the plants through their roots and carried up to the 
leaves, where they are exposed to the air and sunshine, and 
altered so as to become food for the plant. The other 
parts which did not come from the soil he concluded must 
be taken in from the air. These were splendid facts, and 
curiously enough a celebrated English chemist, Dr. Hales 
(born 1677, died 1761), made some similar experiments 
almost at the same time, which confirmed those of Boer- 
haave. Hales even went so far as to measure the quantity 
of water taken in at the roots and given out at the leaves 
of plants, and he discovered the way in which plants breathe 
through the little stomata, or mouths, discovered by Grew 
(see p. 138). 

From the juices of plants Boerhaave next went on to 



194 EIGHTEENTH CENTURY. ft. hi. 

those of animals, and he decomposed in a most beautiful 
and simple manner milk, blood, bile, and those fluids called 
chyle and lymph which convey nourishment to the blood. 
These he compared with the sap, gums, resins, and oils of 
plants, and showed that animal bodies are made up of 
altered vegetable matter, just as plants are in their turn 
composed of matter taken from the soil and the air; and 
he suggested that by careful experiments it would at last be 
possible to discover exactly the materials of which all living 
beings were made. 

Boerhaave's analyses of organic substances were very 
rough and imperfect compared to those which are made now ; 
for you must remember that the four gases, oxygen, hydro- 
gen, nitrogen, and carbonic acid, which we now know are the 
chief constituents of plants, were not yet discovered. Yet 
even these rough attempts were so interesting that students 
.crowded round the doors of his lecture-room for hours 
before the lecture began, to secure admission ; and there can 
be no doubt that his * Elements of Chemistry,' published in 
1732, contained the first steps in the study of the chemistry 
of living things. Boerhaave was also a celebrated botanist. 
He died in 1738, and deserves always to be remembered as 
one of the greatest teachers of the eighteenth century. 



Chief Works consulted. — Brewster's ' Encyclopaedia' — ' Boerhaave ;» 
Miller's 'Organic Chemistry,' 1869; Cuvier, 'Hist, des Sciences 
Naturelles;' Sprengel, 'Hist, de la Medicine,' 1815 ; Burton's 'Life 
and Writings of Boerhaave, ' 1 746 ; Boerhaave, ' Elements of 
Chemistry,' Englished by Dallowe, 1735; Hales' 'Essays concerning 
Vegetable Staticks,' 1759. 



ch. xxiv. HALLE R — ANATOMIST. 195 



CHAPTER XXIV. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

Haller — Foundation of Gottingen University — Rise of Comparative 
Anatomy — John Hunter — His Museum — Bonnet — Spallanzani. 

Haller, 1708-1777. — Among the pupils of Boerhaave there 
was one man who became, in some respects, even more 
famous than his master. This was Albert von Haller, son of 
the Chancellor of Baden, who was born at Berne in 1708, 
and died in 1777. Haller seems to have been a most extra- 
ordinary child ; at nine years of age it is said that he knew 
Latin and Greek, and had written a Hebrew and Greek 
dictionary, a Chaldean grammar, and an historical dictionary ! 
We are not told how good these books were ; but how very 
few boys of nine years old would have been able to write 
them at all ! At seventeen Haller went to Leyden to study 
under Boerhaave, and under Albinus, a famous anatomist ; 
and at nineteen he was already a doctor of medicine. Hav- 
ing been driven out of Paris because the people were 
horrified at "his dissecting dead bodies, he went to Berne, 
where he became professor of anatomy; and in 1736, when 
George II. of England, who was also Elector of Hanover, 
founded the University of Gottingen, he went there as pro- 
fessor of anatomy, surgery, and botany, and soon made that 
University as famous as Boerhaave had made that of Leyden. 
One of his first reforms was to turn the work of his pupils 




J8 



196 EIGHTEENTH CENTURY. pt. iil 

to good account. When medical students are going to pass 
their last examination they are required to write an essay, 
or tJiesis y as it is called, before they can receive their degree 
of doctor. Haller used always at these times to propose to 
each one of his students some difficult point in anatomy or 
physiology, in which he thought new discoveries might be 
made, and he then drew out a plan for them and showed 
them how to begin. By this means their essays were often 
full of new and useful information, and it was a great deal 
owing to the help of his pupils that Haller was able to 
publish 180 volumes on science, all more or less valuable. 
[£ There was also a very good a natomic al theatre at Gbt- 

tingen, and from dissections made there Haller produced 

a a set of most beautiful an atomical drawin gs, which he pub- 
lished between 1743 and 1753. You will remember that 
Vesalius published many fine engravings of parts of the 
human body (see p. 65), and since his time" many others 
had been made, especially by Haller's master, Albinus. But 
Vesalius' drawings were coarse, because he had no micro- 
scope to help him, arid Albinus had only drawn separate 
parts, such as a muscle, a nerve, or a vein. Haller's plates 
were the first which showed the different nerves and vessels 
attached in their right position, and to each plate he added 

W a complete his tory of the functio n, or use of the parts 
1 drawn. He made these drawings so accurate, and spent so 
I much time upon each minute structure, that in seventeen 
years, with all the help he had, he was not able to complete 
the description of the whole human body. 

Haller discovers the Power of the Missies to 

} % Contract. — It was while he was at work at these dissections, 
that he made one great discovery, which you must try to 
understand. If you clasp your right hand round your left 
arm, just above the elbow, and then bend your left arm, you 



*>* 



ch. xxiv. COMPARATIVE ANATOMY. 197 

will feel the part under your hand swell up and grow hard. 
The reason of this is that the muscle of your arm, called the 
biceps, has contracted, or grown shorter and thicker, in the 
process of bending your arm. If you open your arm again, 
the swelling will go down, because the muscle is stretched out. 
Now before Haller's time it was thought that the muscles 
could not contract of themselves, but were drawn up by the 
nerves. Haller discovered that this is not so, but that a 
muscle, if irritated, will draw itself together, even when it is 
quite separated from the nerves, and this has since been 
proved to be true by a great number of experiments. So 
that though it is true that our nerves are the cause of our 
moving, because they excite the muscles and so make them 
contract, yet the real power of contraction is in the muscle 
itself. 

Com parat ive Anato my, or the Comparison of Dif- 
ferent Structures in Men and Animals.— John Hunter. 
— Another point in which Haller did good service to science 
was in comparing the same parts of the body of men and 
animals, and showing how far they are alike. This study, 
which is called the study of compai'ative anatomy, has now 
become very important, for by examining any organ, such as 
the heart, for example, from the lower animals in which it is 
very simple, up to man in whom it is complicated, we can 
trace its gradual improvement, and understand it much more 
perfectly. Aristotle and Vesalius had both of them com- 
pared some of the parts of different animals, and so had 
other and later zoologists ; but Haller was the first to make 
it a regular study, and John Hunter, who lived about the 
same time, devoted his whole life to it, and raised it to the 
rank of a separate science. 

John Hunter, who was born in the County of Lanark, 
in 1728, was the brother of a very eminent London phy- 



rp^ 



n 



y, 



198 EIGHTEENTH CENTURY. pt. hi. 

sician, Dr. William Hunter, who was also a great anatomist. 
John, being delicate, had been allowed to grow up with very 
little education, and at twenty years of age he came up to 
London, a mere ignorant lad, to try and help his brother in his 
anatomical dissections. Here he soon showed that he had 
plenty of ability, for he learnt dissecting so rapidly that at 
the end of a year he was able to teach his brother's pupils, 
and before long he became one of the leading surgeons at 
St. George's Hospital, and had a large private practice. 

But though he made a great deal of money by his pro- 
fession, he s pent it a ll upon hi s favourite study of anatomy, 
to which he devoted every spare moment. His great wish 
was to compare thoroughly the different parts of men and 
animals, so as to show how the life of each one of them is 
carried on. For this purpose he dissected and preserved in 
different ways all the bodies of animals upon which he could 
lay his hands. He bought up all the wild beasts that died in 
the Tower, where they were then kept, and any which he 
could procure from travelling menageries, and he even kept 
foreign animals himself in a piece of ground at Earl's Court, 
Brompton, that he might watch their habits and dissect their 
dead bodies. 

As years went on and his specimens increased, he built a 
large museu m in Leicester Square, and arranged his collec- 
tion so as to show which parts in different animals serve for 
the same use. For example, to illustrate the way in which 
animals digest their food, he placed first the hydras, polyps, 
and sea-anemones, which are all stomach, being in them- 
selves nothing but a simple bag surrounded by little feelers, 
and having a fluid inside which dissolves the food. Then 
he arranged in order many forms up to the leech, which is 
a bag with two openings, and has a head and nerves and 
other parts, besides a stomach. Then came the insects, 



ch. xxiv. HUNTER'S MUSEUM. 199 

some of which, as the bees, have a separate receptacle for 
honey, of which they disgorge a part and then pass on the 
rest into the real stomach. Then came the snails, in which 
the stomach is a separate part with a second opening to 
pass out the food it cannot take up. Then the fishes, some of 
whom have stomachs strong enough to crush the shells and 
indigestible parts of their food, while others have the mouth 
lined with teeth for this purpose ; then came the stomachs 
of reptiles; and afterwards those of birds, .with the curious 
crop where the food lies first, and the gizzard, in which it is 
rubbed against the little stones which the bird swallows. 
Then finally came the stomachs of the higher animals, with 
many curious and interesting peculiarities ; as, for example, 
the divided stomach of those animals, such as the cow, which 
chew the cud, and of the camel, in which one division serves 
as a water-bag. And side by side with these organs of 
digestion he placed the teeth of each animal, showing how 
these were each exactly fitted- to prepare the food for the 
particular kind of stomach of the animal to which they 
belonged. 

In this way Hunter tried to arrange the history of all the 
different organs of the body, tracing out each as perfectly as 
he could, and showing how it suited the wants of the various 
animals. His museum cost him an immense amount of labour, 
and more than ^70,006 in money ; when he died, in 1793, 
it was bought by the English Government for ;£i 5,000 and 
placed in the London College of Surgeons, and since then 
many a London student of physiology has had occasion to 
be thankful to the rough and uneducated John Hunter for 
the laborious and careful work he did, and the magnificent 
collection he left behind him. 

Experiments upon Animals by Bonnet and Spallan- 
zani. — While Haller and Hunter by their dissections were 



EIGHTEENTH CENTURY. 



PT. III. 




> 



adding greatly to our knowledge of the structure of animals, 
two famous naturalists in Switzerland and Italy were bringing 
o light some extremely curious and interesting facts about 
their growth. 

The first of these, named Charles Bonnet, was born at 
Geneva in 1720, and died in 1793. He had a great love of 
natural history, and when he was twenty years of age he 
wrote a paper upon aphides, or plant-lice, which was so re- 
markable that the French Academy of Sciences at once 
elected him one of their corresponding members. He 
also made some very interesting experiments upon plants, 
showing that they have the power of seeking out for them- 
selves what is necessary for their growth. We all know that 
plants grow towards the light, and if kept in a dark room 
will seek out even a crack through which the light comes. 
But Bonnet proved that they will do much more than this, 
for he found that if he twisted the branch of a tree so as to 
turn the leaves bottom upwards, in a little time each leaf 
turned right round on its stalk so as to get back into its 
natural position ; while on the other hand, if he hung a wet 
sponge over a leaf, the leaf would turn its under side up- 
wards, so as to bring the little mouths, or stomata, close to 
the sponge, and enable them to drink in the water. In this 
way a plant will always find out the best way of growing so 
as to get as much sun and food as it can. Many curious 
facts of this kind were published in Bonnet's work on the 
' Use of the Leaves of P lants,' but what I wish now particu- 
larly to relate to you are his experiments upon animals and 
the regrowth of limbs which had been cut off. 

It had long been known that very simple organisms, such 
as polyps, may be cut in pieces, and each part will live and 
become a perfect creature ; but no one thought it possible 
that any of the more complicated living beings could be 



CH. xxiv. BONNET AND SPALLANZANI. 201 

treated in this way. Bonnet, however, and the famous 
Italian naturalist Spalla nzani (1720-1700) proved by a great 
number of experiments that tails, legs, and even heads will 
grow again in some animals, after they have been cut off. 
The garden-worm, for example, is an animal with many 
organs : it has numerous bristles, which serve as feet, it has 
arteries and veins, nerves, and organs of digestion, and a 
mouth ; yet Bonnet found that a worm if cut in pieces would 
grow a new head or a new tail, and, what was still more 
curious, in some rare cases it grew the head on the end where 
the tail had been before ! Spallanzani went even farther, 
for he experimented on snails. Now the common garden 
snail has a head with four horns, moved by very complicated 
muscles, and two of these horns have eyes at the end ol 
them ; moreover it has a mouth, with a horny jaw and a 
tongue armed with innumerable small teeth. Spallanzani 
cut off first the horns with eyes, and afterwards the mouth 
and tongue, and found that the snail had power to re-grow 
them all. He then tried upon aquatic salamanders, which 
resemble our newts, or efts. These creatures have red blood 
like ourselves, they have a heart, lungs, bones, and muscles, 
and their legs possess muscles and nerves like those of a 
man ; yet Spallanzani cut off the tail and legs of one sala- 
mander six times in succession, and in another case, Bonnet 
cut them off eight times, and they grew again. Bonnet even^^W^*^* 
took out the right eye of a newt, or eft, and in eight months i) ~ jl ^' *t 
another eye had grown in its place. Th ese experiments wer e £5<^w^ 
very startling, for the v showed that the lif e of the_lojyer 
animals does not so much depend on a particul ax. part of 
the body, as it do es in ourselv es and in the higher animals. 
If you cut off the head of a man or an ox, they die, or if you 
cut off a leg, it never grows again ; but these experiments 
proved that the worm and the snail live and grow new 



K> 




I I - 

1 - 



202 EIGHTEENTH CENTURY. pt. hi. 

heads and limbs, and that the more simple an animal is, the 
more power it has to live and grow after it is cut in pieces. 
These discoveries led Bonnet to make a suggestion which 
hould be remembered, because it has become of great 
TKr importance in the present study of natural history. He 
asked whether it was not likely that there was a gradual de- 
velopment or complication of the parts of the body as you 
J ascend from the lowest plant up to the highest animal, so 
Ithat the body of a worm, for example, could do all the work 
necessary to keep it alive and make it grow, without the 
help of its head, and a lizard could in the same way make a 
new leg without much difficulty. But as the machinery grew 
more and more complicated this would not be so easy, till 
at last it would become impossible in the higher animals, 
just as in a complicated machine one broken wheel will 
upset the whole working. Bonnet wrote a book called 'The 
Contemplation of Nature, 7 in which he dwelt upon this 
subject, and tried to trace out how animal forms had become 
gradually higher and higher, till they had arrived at man. 
We shall see by and by how this idea occurred also to the 
naturalist Lamarck, and how it has become the foundation 
of a grand theory of life in the present century. Meanwhile 
you must bear in mind that Bonnet and Spallanzani added 
enormously to our knowledge of the lower animals and their 
powers of life, and together with Boerhaave, Haller, and 
Hunter did a great deal to advance the sciences of anatomy 
and physiology in the beginning of the eighteenth century 7 . 

Chief Works consulted. — ' Life of Haller' — ' Naturalists' Library f 
Brewster's 'Encyclopaedia,' arts. 'Physiology' and ' Haller ;' La wrence's 
'Lectures on Comparative Anatomy,' 1816 and 1848; Lawrence's 
Translation of Blumenbach's ' System of Comparative Anatomy,' 1807; 
* Life of John Hunter' — ' Naturalists' Library,' vol. x. ; Cuvier, ' Hist, 
des Sciences Naturelles ; ; Carpenter's 'Comparative Physiology;' Tom 
Taylor's ' Leicester Square,' Appendix by Professor Owen. 



CH. xxiv. DEVELOPMENT OF ANIMALS. 203 



CHAPTER XXV. 

Buffon and Linnaeus compared — Buffon on Natural History — Dauben- 
ton — Linnaeus — Linnaean or Artificial System — Natural System — 
Character and Death of Linnaeus. 

Advance of Natural History — Buffon and Linnseus. — 

In the year 1707 two men were born, the one in France 
and the other in Sweden, whose names have become almost 
equally well known, although they were by no means equally 
great. 

The Frenchman, George-Louis Le Cle rc Buffo n, the son 
of a counsellor of the parliament of Dijon, was born on his 
father's estate in Burgundy. The Swede, K arl Lin nseus, the 
grandson of a peasant and son of a poor Swedish clergy- 
man, was born in a small village called Rashult, in the south 
of Sweden. Buffon enjoyed the best education which 
France could afford him, with plenty of opportunity to culti- 
vate his love of natural history. At one-and-twenty he 
succeeded to a handsome property, and after travelling for 
some time, settled down to a life of ease and literature, partly 
in Paris, and partly on his estate in Burgundy. Linnaeus 
was taught in a small grammar-school, where he showed so 
little taste for books that his father would have apprenticed 
him to a shoemaker, if a physician named Rothmann, who 
saw the boy's love for natural history, had not taken him 
into his own house and taught him botany and physiology. 
At one-and-twenty, when Buffon came into his fortune, the 



204 EIGHTEENTH CENTURY. PT. HI. 

young Linnaeus, with an allowance of eight pounds a year 
from his father, was a struggling student at the University 
of Upsala, putting folded paper into the soles of his old 
shoes to keep out the damp and cold. 

Buffon 's Work on Natural History: he traces the 
Distribution of Animals. — Buffon's private life is not 
interesting. He was a vain man, and not a moral one ; but 
he had great talents, and remarkable perseverance and 
industry. In 1739 he was appointed Superintendent of the 
Royal Garden and Cabinet at Paris, a position which he 
held till his death. His great work, of which we must now 
speak, was his ' Natural Histor y.' which occupied him during 
the greater part of his life. It is one comp rehensive history 
of the living world, containing descriptions of all the animals 
then known, their structure, their distribution, their habits, 
and their instincts, and, mingled with these, many curious 
theories about the world and its inhabitants. 

The anatomical part of this work was done by a physician 
named Daubenton, who came from Buffon's own village, and 
was appointed keeper of the cabinet of natural history 
through his influence. Buffon was very fortunate in having 
the help of this man, for having weak sight himself, and 
being more fond of general theories than of minute details, 
this part of his work would have been very poor if it had 
not been for Daubenton's careful and conscientious dis- 
sections and descriptions. The rest of the work was written 
chiefly by Buffon himself, who bestowed upon it immense 
pains and labour. He was a very pleasing writer, and did a 
I great deal for natural history by making it popular. His 
/j}ooks were more like romances than works of science, but 
he collected in them a great deal of very useful information, 
and put it in a shape which every one could read with 
pleasure, and in this way led people to think, and to wish to 



ch. xxv. EARLY LIFE OF LINNAEUS. 205 

know more about natural history and the habits and lives ^Oi ^y^^ 
of animals. He was also the first to trace out with any care j\ 
the way in which animals are distributed over different parts 
of the globe; how they are checked by climate, by | 
mountains, by rivers, and by seas from wandering out of I 
their own regions, and how they are more widely spread 
over cold countries than over warm ones, because they are 
able to cross the seas and rivers upon solid or floating ice, 
and so get from one region to another. 

In this general way Buffon gathered together a great 
many interesting facts about animals. His works were all 
the more popular because he disliked anything like classi- 
fication. He would not attempt to group the animals after 
any particular method, but liked to describe each one with 
a little history of its own, and to write on freely without any 
very great scientific accuracy. Of course the consequence 
was that he often made great mistakes, and arrived at false 
conclusions; still he had so much genius and knowledge 
that a great part of his work will always remain true, and 
Natural History owes a great deal to BufFon. He died in 
1788, in the eighty-first year of his age, and twenty thousand 
people assembled to do him honour at his funeral. 

Life and Influence of Linnseus, 1707-1778. — We 
must now turn to Linnseus, whose whole life and labours 
were as different from those of Buffon as his birth and early 
life had been. Buffon hated to be bound down to exact _^_ 
details ; Linnaeus found his greatest pleasure in tracing out -^~^ 
each minute character in plants and animals so accurately as 
to be able to build up a complete classification, by which 
any one could tell at once to what part of the animal or 
vegetable kingdom any living being belonged. While Buf- 
fon's books were entertaining and readable, Linnaeus's were 
often hard dry science, consisting chiefly of long accurate 



& 



206 EIGHTEENTH CENTUR Y. pt. hi. 

tables and minute details about the structure of animals and 
plants. Yet Linnaeus's writings are worth infinitely more 
than those of Buffon for one simple reason, he had a more 
earnest love of truth. 

Linnaeus seems to have been born a botanist. He writes 
in his diary that when he was four years old he went to 
a garden party with his father and heard the guests . dis- 
cussing the names and properties of plants; he listened 
carefully to all he heard, and ' from that time never ceased 
harassing his father about the name, quality, and nature of 
every plant he met with,' so that his father was sometimes 
quite put out of humour by the incessant questioning. 
However at last, when Dr. Rothmann took him into his 
house, he had opportunities of learning, and from that time 
he advanced so rapidly that he was soon beyond all his 
teachers. 

In 1736, after meeting with many kind friends in his 
poverty, and making a journey to Lapland, which was paid 
\fi#r by the Stockholm Academy of Science, he went to 
Holland. Here he called on the celebrated Boerhaave, who 
with his usual good nature introduced him to a rich banker, 
named Clifford, who was also a great botanist. This was 
the turning-point of Linnaeus's life. Mr. Clifford invited 
him to live with him, treated him like a son, and allowed 
him to make free use of his magnificent horticultural garden. 
He also sent him to England to procure rare plants, and 
gave him a liberal income. It was at this time that 
Linnaeus is said to have been so overcome by the sight of 
the mass of golden bloom on the furze at Putney Heath, 
that he fell upon his knees and thanked God for having 
created a plant of such wondrous beauty. Linnaeus con- 
tinued with Mr. Clifford for some time, till his health began to 
fail, and he found besides that he had learnt all he could in 



ch. xxv. LINNMUS ON SPECIES. 207 

this place, so he resolved to leave his kind friend and wander 
farther. Mr. Clifford seems to have been much hurt at his 
leaving, yet he continued his kindness to him through life. 

Linnaeus went to Leyden and Paris, and from theie to 
Stockholm, where he practised as a physician, and at last he 
settled down as Professor of Medicine and Natural History 
at Upsala, where he founded a splendid botanical garden, 
which served as a model for many such gardens in other 
countries, such as the Jardin de Trianon in France, and 
Kew Gardens in England. His struggles with poverty were 
now over for ever, and his fame as a botanist was spread all 
over the world. He used to set out in the summer days 
with more than 200 pupils to collect plants and insects in 
the surrounding country, and many celebrated people came 
to Stockholm to attend Linnaeus's ' Excursions.' Then as his 
pupils spread over the world he employed them to collect 
specimens of plants and animals from distant countries, and 
he himself worked incessantly to classify them into one 
great system. 

Linnaeus gives Specific Names to Plants and 
Animals. — And now we must try to seize upon the chief 
points of Linnaeus's work, in order to understand some- 
thing of what he did for science, although it is quite impos- 
sible in a book of this kind to give even a sketch of his 
divisions of the animal and vegetable kingdoms. The first 
and greatest point of all was that he gave a second or specific 
name to every plant and animal. Before his time botanists 
had only given one name to a set of plants • calling all roses, 
for example, by the name Rosa, and then adding a descrip- 
tion to show which particular kind of rose was meant. 
Thus, for instance, for the Dog-rose they were obliged to 
say Rosa, sylvestris vulgaris, flore odorato incarnate, that is, 
' common rose of the woods with a flesh-coloured sweet- 



208 EIGHTEENTH CENTURY. PT . in. 

scented flower.' This, you will see, was extremely incon- 
venient ; it was as if all the children in a family were called 
only by their father's name, and you were obliged to describe 
each particular child every time you mentioned him; as 
'Smith with the dark hair,' or i Smith with the long nose and 
short fingers,' etc. A botanist named Rivinus had suggested 
in 1690 that two names should be given to plants, and 
Linnaeus was the first to act upon this idea and to give a 
specific, or, as he called it, trivial name to each par- 
ticular kind of plant, describing the plant at the same 
time so accurately that any one who found it could decide at 
once to what species it belonged. To accomplish this he 
classified all plants, chiefly according to the number and 
arrangement of their stamens and pistils (or the pollen-bear- 
ing and seed-bearing parts), and then he subdivided them 
by the character and position of their leaves and other parts. 
In describing the geranium, for example, he mentions 
first the * sepals,' or little green leaves under the flower ; he 
says they are five, and very pointed ; then the ' petals,' or 
flower-leaves, are five also, growing on ,the sepals and 
heart-shaped ; the ( stamens ' are ten in number, and grow 
separate ; the little vessels on the top of the stamens, which 
are called * anthers,' and hold the yellow dust, are oblong ; 
the * pistil,' or seed-vessel, is formed of five parts, which 
are joined together into one long beak ending in five points ; 
the seeds are covered with a skin and are shaped like a 
kidney, having often a long tip which is rolled round in a 
spiral (like a corkscrew). Here we have a definition of 
the genus geranium ; but many geraniums will answer to 
this description, so he goes on to describe some more 
special characters. The sepals in this particular specimen, 
he says, are 'joined together in one piece; the stem of the 
plant is woody, the joints are fleshy, the leaves are slightly 



ch. xxv. LINN&AN SYSTEM. 209 

feathered at the edge. These last characters are peculiar to 
this kind of geranium, which he calls Geranium gibbosum, 
and here we have the specific name. Any geranium which 
has the woody stem, the joined sepals, the fleshy joints, 
and the feathery-edged leaves, will be the species called by 
Linnaeus gibbosum. 

You will see that by this system it is always possible to 
find out easily to what part of the vegetable kingdom your 
plant belongs, and what its name is ; and if, after you have 
traced its genus, there is no species which exactly agrees 
with yours, you then know that you have discovered a new 
species which has not been described before. Linnaeus 
classified animals after this same plan, quadrupeds chiefly by 
their teeth, and birds by their beaks and feet, and after his 
system was complete, any one could discover the scientific 
name of a plant or animal by exercising a little care and 
patience. This system is called the Linnaean or artificial 
system, because it only selects a few particular parts of a 
plant, so as to help you to look it out in a kind of diction- 
ary. It tells you very little of the real or natural life of 
the plant, and often brings some very near together which 
are really very different It is as if you classified people 
by some particular feature, such as those who had long 
hair, or short hair, dark or light, curly or straight. This 
might be very useful for recognising them, but it would be 
quite artificial, and would tell you very little about their 
real relationship. Therefore this classification has now 
been partly set aside for another or natural classifica- 
tion, which Linnaeus also suggested, only he thought 
it too difficult for ordinary people; and which was 
worked out by a French botanist named Jussieu, as we 
shall see by and by. But the Linnaean system is still 
extremely useful for finding the name of a plant or animal, 



210 EIGHTEENTH CENTURY. ft. hi. 

and many people in the last century were led to study 
zoology and botany by the simplicity of the classifications 
of Linnaeus. 

The other useful point in Linnaeus's system was the 
accurate and precise terms he invented for describing plants. 
Before his time naturalists used any words which suited 
them, and as different people have often very different ideas 
as to what is meant by long or short, round or pointed, etc., 
the descriptions were often of very little value. But 
Linnaeus could not work out his system without using very 
clear terms and explaining beforehand what he meant by 
them; and as his nomenclature, or system of names, was soon 
followed in other countries, botanists in all parts of the 
world were able to recognise at once what was meant by the 
description of any particular plant. The same advantage 
arose out of his classification of animals, and the care with 
which he traced out their chief characters. * I wish I could 
have given you some idea of this system, which was fully 
explained in the * Systema Naturae,' completed in 1768. But 
when you remember that Linnaeus classified minutely the 
whole of the animals and plants known in the world, you 
will perceive that it would be necessary to write a separate 
book to make it intelligible. If you can only remember 
that he did build up this artificial system, and that he was 
the first to give specific names to plants and animals 
and to create an accurate nomenclature all over the 
world, you will, I think, have learnt as much as you need 
know at present about the work of the great Swedish 
naturalist. 

Linnaeus was not a vigorous old man. The hard 
struggles of his youth and the immense work of his after- 
life had worn him out, and at fifty-six he was obliged to ask 
the King of Sweden to let his son lecture sometimes in his 



CH. xxv. LINN JEAN COLLECTION. 21 1 

place. With this help he continued to work at science till 
within two years of his death, when his mind became feeble. 
He died in 1778, loaded with honours and beloved and 
esteemed by the greatest men all over the world. His had 
been a noble life ; enthusiastic and truth -loving, he had 
worked, even when he was poor, for science and not for 
wealth, and when he became famous and rich he helped his 
pupils as others had helped him, and lived simply and 
frugally till his death. Unlike Buffon, his private life was as 
pure as his public life was famous. Over the door of his 
room he placed the words ' Innocue vivito, Numen adest 1 
(' Live innocently, God is present '), and he lived up to his 
motto. His study of nature had filled him with deep 
reverence and love for the Great Creator, and he used 
often to tell his friends how grateful he was to God for 
those gifts which had made his life so full of interest and 
delight. 

After the death of Linnaeus his family sold his collection 
of plants and insects, and all his books and manuscripts, 
to Dr. James Edward Smith (afterwards Sir J. E. Smith), 
for one thousand pounds. The King of Sweden was at 
this time away from Stockholm, but directly he returned 
and heard that such a valuable national treasure was on 
its way to England he sent a man-of-war to try and bring 
it back. A very amusing chase then took place; Dr. 
Smith did not mean to lose his prize if he could help 
it, so he set full sail and literally ran away till he reached 
the Thames, and landed safely in London without being 
caught. Thus the Linnsean collection came to England, 
and is now in Burlington House. The Swedes are natu- 
rally sorry that it left their country, but, on the other hand, 
it has become more known to scientific men in London 
than it could ever have been in Stockholm. 
11 



EIGHTEENTH CENTUR Y. pt. hi. 



With Linnaeus we must end for the present the history 
of the sciences relating to living beings. Early in the nine- 
teenth century we shall return to them again, but in the 
next chapter we must learn something of a new science 
which arose about this time ; namely, the science of 
* Geology,' or the study of the earth. 



Chief Works consulted. — Jardine's 'Naturalists' Library,' vols. ii. and 
xiii. ; Brewster's 'Encyclopaedia' — 'Buffon and Linnaeus;' Cuvier, 
' Histoire des Sciences Naturelles;' Smith, Sir J., 'Introduction to 
Botany j ' Pulteney's ' View of Writings of Linnaeus ; ' Linnaeus, 
' Systema Naturae.' 



ch. xxvi. GEOLOGY. 213 



CHAPTER XXVI. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

Prejudices concerning the Creation of the World — Attempts to Account 
for Buried Fossils — Palissy — Scilla — Woodward — Vallisneri — 
Lazzaro Moro — Werner — Disputes between the Neptunists and 
Vulcanists — Hutton — William Smith ; His Geological Map of 
England. 

Early Prejudices concerning the Formation of the 
Rocks. — You will no doubt remember that when we were 
speaking of the science of the Greeks, we learnt (p. n) that 
Pythagoras made many interesting observations about the 
crust of the earth, which led him to say that the sea and 
land must have changed places more than once since the 
creation of the world. Especially he pointed out that sea- 
shells are found inland, deeply buried in the hills ; and that 
the sea eats away land on the coast in some places, while in 
others earth is washed down by the rivers and laid at the 
bottom of the ocean. 

We have now passed over more than 2000 years since 
the time of Pythagoras, and you will notice that we have 
heard nothing more about observations of this kind. The 
fact is, that during the Dark Ages, the study of the earth had 
been almost entirely neglected, and people had taken up 
the mistaken notion that they ought to believe, as a matter 
of faith, that the world was created in the beginning just as 
we now see it But knowledge and inquiry were advancing 



214 EIGHTEENTH CENTURY. ft. hi. 

so fast in the eighteenth century, that it was impossible for 
such ignorance to continue long. People could not go on 
digging wells and making mines in all parts of the world 
without being struck by the way in which the different strata, 
or layers of rock, are arranged in the earth's crust, nor 
without noticing the fossil shells, plants, and bones of 
animals which they found buried at great depths. 

At first they were very unwilling to believe that these 
remains had ever belonged to living animals and plants, and 
they tried to imagine that they were only stones resembling 
shells, leaves, etc., which had been in some way mysteriously 
created in the earth. Then, when this absurd idea was 
given up, they next inquired whether a universal flood 
might not have spread them over the land ; but though this 
opinion was upheld for more than a hundred years, yet it 
was clear to all those who really studied the subject that it 
could not account for the many layers of different fossils 
deeply buried in the earth. 

First Attempts to study the Fossil Remains and the 
Beds containing them. — At last, little by little, there arose 
men who adopted the more sensible plan of studying the 
different formations in the crust of the earth before making 
theories about them. Bernard de Palissy, the maker of the 
famous French pottery, was the first to assert, in 1580, that 
the fossil shells were not only real sea-shells left by the 
waters of the ocean, but that they belonged to marine 
animals which had lived and died on the spots where they 
were found, and had not been strewn at random over the land 
by a deluge; then, in 1669, we find Steno, a Dane, writing 
a remarkable work on petrifactions in the rocks ; and in 
1670 Scilla, an Italian painter, published a treatise on the 
fossil shells and other remains in the rocks of Calabria, and 
made some beautiful drawings of these remains, which mav 



ch. xxvi. GEOLOGY. 215 

now be seen in the Woodwardian Museum at Cambridge. 
Next we find our own scientific men — Hooke, the naturalist 
Ray, and a famous geologist Dr. Woodward — speculating why 
the earth's crust is made up of different layers, one above 
another, with different fossils in each ; while Ray pointed 
out that a flood could not lay the fossil remains in great 
beds in particular places as they are found ; but that there 
is every proof that the animals must have lived there for 
many succeeding generations. Woodward (1695) also made 
a careful collection of specimens of chalk, gravel, coal, 
marble, and other rocks, together with the fossils which he 
found in them ; these are also in the Cambridge Museum. 
But all these men, though they did good work, still held 
many erroneous notions about the way in which the crust 
of the earth had been formed. 

The first geologists who gave any real explanation of the 
facts were Vallisneri and his friend Lazzaro Moro, an Italian, 
born at Friuli in Lombardy, in 1687. Moro pointed out, 
as Woodward had done before him, that the different strata 
lie in a certain order one above the other, and that within 
them are imprisoned fossil fishes, shells, corals, and plants, 
in all countries, and at all heights above the sea. The 
rocks, said Moro, writing in 1740, must have been soft 
when these fossils were buried in them, and some must have 
been deposited by rivers, because they contain fresh-water 
animals and plants ; while others contain only marine fossils, 
and must have been laid down under the sea. It is clear, 
then, that they must all have been formed in lakes or seas, 
and have been raised up by earthquakes, or thrown out by 
volcanoes, such as we see taking place from time to time in 
the world now. This explanation, though rough, was true, 
and ^loro deserves tr r b^ rerr| emhered a s prig °f f ^ p fi r ^ men 
who led the way towards a true study of the earth. After 



2i6 EIGHTEENTH CENTURY. ft. hi. 

him there followed many others, whom we cannot mention 
here ; but the next whose name is famous was the great 
Werner, professor of mineralogy at Freyberg in Saxony. 
— Werner calls attention to G-eology, 1775. — Abraham 
Werner, the son of an inspector of mines in Silesia, was 
born in 1750. His first playthings were the bright minerals 
which his father's workmen gave him, so that he knew them 
by sight, even before he could tell their names ; and as he 
grew up he seemed to care for nothing but mineralogy and 
the wonderful facts it revealed about the formation of the 
earth. Freyberg, when he first began to lecture there, in 
1775, was only a small school for miners ; but it was not long 
before he raised it to the rank of a university, so great was 
the fame of his lectures. He pointed out to those who came 
to learn of him, that the study of the rocks was something 
more than merely searching for minerals ; and that the crust 
of the earth was full of wonderful histories, which might be 
read by those who cared to take the trouble. He pointed 
out how some formations were stratified, that is, arranged in 
layers, and contained fossil shells and other organic remains ; 
while, on the other hand, some were unstratified, and had 
no fossils in them. Some rocks were bent, as in Fig. 37 ; 




- Fig. 37. 
Diagram of Bent Rocks. (Page.) 

others had been snapped asunder and forced one up and 
the other down, as in Fig. 3 8 ; and he bade them try to seek 
out the reason of these bendings and breakings of the earth's 
crust. He reminded them also that mining was one of the 
great roads to wealth, and that even the history of nations 
often depended upon the kind of ground which they had 



ch. xxvi. WERNER ON GEOLOGY. 217 

•__ — , 

under their feet By facts such as these he opened men's 
eyes to see the wonders of the earth's crust, so that people 
began to talk everywhere of the geological lectures of Werner, 




Fig. 38. 

Diagram of rocks which have been rent apart at the point,/, and tilled up. I, I, 2, v y 

etc., Beds which before the disturbance were continuous. 1 

and numbers flocked from distant countries, and even learnt 
the German language, that they might come and hear him. 

In this way he spread the love of geology all over 
Europe. He was so eager and earnest himself that his pupils 
could not fail to catch some of his enthusiasm, and to try to 
follow out his ideas. But, unfortunately, this very enthu- 
siasm led him to insist upon a theory which kept back his 
favourite science for many years. 

Neptunists and Vuleanists. — Werner had only studied 
a small part of Germany, and there were then very few de- 
scriptions of other parts of the world which he could read ; 
and so, from want of knowledge, he formed the mistaken 
idea that in olden times, after the globe had cooled down 
and become fit for living beings, there were no volcanoes 
for long ages, but that basalt and other rocks, which we 
now know were made by volcanic heat, were all laid down 
by water. There were men living in Werner's time who 
knew that this was a wrong theory, but he would not listen 
to their arguments, and the two parties became so violent 
that many years were lost in angry disputes between the 
NeptunistS) or those who thought all rocks were laid down 
by water, and the Vulcanists, who contended that many rocks, 
such as basalt, were made by volcanic heat. 

1 Kindly drawn for me by Professor Ramsay. 



3i8 EIGHTEENTH CENTURY. pt. hi. 

Hutton teaches that it is by the Study of Changes 
going on now that we can alone learn the History of the 
Past. — While these discussions were going on upon the 
Continent, a Scotchman was setting to work in the right 
way to settle the question. This man was Dr. Hutton, 
one of the greatest geologists that has ever lived ; and the 
reason of his greatness was the same which we have found at 
every step in our history of science. Before he made any 
theory he sought out the facts. He travelled and observed 
for himself, he collected patiently details about the layers or 
strata in the formations of all countries through which he 
passed ; and it was only after all these investigations that in 
1788, when he was sixty years of age, he wrote his famous 
1 Theory of the Earth,' in which he showed how the history 
of the earth's crust might be traced out. This work, al- 
though very interesting, was not much read; but one of 
Hutton's favourite pupils, the celebrated Dr. Playfair, wrote 
a book called ' Illustrations of the Huttonian Theory,' by 
means of which Hutton's opinions became well known. 

About Hutton himself there is very little to tell. He was 
born in Edinburgh in 1726, studied medicine, and took his 
doctor's degree in Leyden in 1749, and then returned to 
Edinburgh, and devoted all his life to science. Of his 
teaching I should like to write a great deal, but we must 
content ourselves with a little which can be easily under- 
stood. His great principle was that it was useless to try and 
guess how the rocks had been made and fossils buried in 
them, for this had only led to endless confusion and dis- 
putes. Men must go, he said, and see with their own eyes 
how different strata are being formed now, how rivers and 
glaciers are carrying down earth and stones from the moun- 
tains into the sea, and how volcanoes are throwing out- 
melted matter which cools down into hard rock; and then 



ch. xxvi. AQUEOUS ROCKS. 219 

they must compare these with the older rocks in the crust 
of the earth, and see whether they were not formed in the 
same way. 

Aqueous (or water-made) Rocks. — When we find a 
piece of marble made up almost entirely of oyster and other 
shells, and of pieces of coral, we cannot doubt that it must 
once have been a heap of loose shells and corals such as we 
now see on the shore or under the water, and that it has since 
been hardened into limestone. When we find that by 
crushing or scraping sandstone we can turn it into sand like 
that which we see on the seashore, and which we know has 
been made by the sea grinding the stones and rocks of the 
beach against each other, then we cannot doubt that the 
sandstone has once been loose sand, and before that was 
part of a rock which has been ground down by the waves. 

And so we are led to the conclusion that the rocks of 
our earth, as we see them now, have been formed out of the 
materials of still older rocks which existed before them, and 
are being gradually moulded into other and newer rocks, 
which will exist when these have been destroyed. Our solid 
earth is being wasted every day. The sides of the moun- 
tains are washed down and their materials are carried through 
the valleys by the running water. In this way the soil is 
brought down to the coast, and here it is eaten away by the 
waves of the sea, and falls to the bottom of the ocean, out 
of which it will be raised again by earthquakes, volcanoes, 
and other movements of the earth's crust, such as can be 
proved to be going on in parts of the world at this day. As 
far back as investigations and reasoning can go we find 
everywhere signs that these gradual and incessant changes 
have always been going on, and that the face of our earth, 
as we now see it, has been moulded out of the ruins of an 
older world 



220 eighteenth century. n. m. 

Igneous (or heat-made) Hocks.- — But how are we to 

decide about those rocks, such as basalt, which Werner 
thought were made by water ? Hutton was convinced they 
were formed in volcanoes ; and yet it was true that they did 
not contain bubbles of air as lava does, which has poured 
down the sides of a volcano in the open air. Here his 
friend and pupil Sir James Hall came to his assistance by 
melting pieces of rock in his chemical laboratory, and letting 
them cool down under very heavy pressure. When this was 
done they could hardly be distinguished from pieces of 
basalt which he took out of the earth. It is clear, there- 
fore, he said, that these rocks have either cooled down in- 
side the volcano, with a great weight of rocks above them, 
or have been poured out under the sea, which would press 
down heavily upon them and shut out the air. 

Another question which Hutton cleared up in the same 
way was that of the formation of granite. Werner believed 
that all the granite rocks, of which you may see plenty in 
different parts of the world, were made first, before any other 
rocks were laid down by water. Hutton did not think this 
was true, but that, on the contrary, granite might be even 
now forming deep down within the crust of the earth. But 
how was he to prove this ? He said to himself, * If melted 
granite forms under the softer strata which have been laid 
down by water, it ought occasionally to obtrude itself into 
them in narrow wedges when it is expanded by heat, and I 
shall be able somewhere to find veins of granite piercing the 
rocks above.' 

To prove whether this was so he made a journey to the 
Grampians, where there are large masses of granite ; and 
there, in Glen Tilt, he found the veins of red granite branch- 
ing out into the clay- slate and limestone rocks above, as 
in Fig. 39. It is easy in this diagram to see that the 



CH. XXVI. 



IGNEOUS ROCKS. 



221 



water-made layers, a b, must have been there before the 
granite was melted, otherwise it could not have sent the 
straggling veins, c c, up into them. And so he convinced 
himself that some granites are newer than the aqueous rocks 




Fig. 39. 

Granite Veins in Glen Tilt. 

a. Clay slate, b. Limestone, c. Granite veins. 

which lie above them. It is said that he was so delighted 
at finding this proof that the guides who were with him 
thought he had discovered a vein of gold. 

This is one out of many examples of the way in which 
Hutton worked and corrected the mistakes which had 
sprung up in the German school of geology. Werner had 
taught his pupils that there was really something to be learnt 
from the study of the rocks ; that they could be made to 
tell real histories of the past and help men to get wealth for 
the future, and thus he persuaded them to give time and 
thought to this work. Hutton showed that to carry on this 
study rightly they must open their eyes to all that is going 
on now, and that the only way to read the history of the 
past is to compare it with the present. 

"William Smith surveys the Bocks of England. — 
Meanwhile another man, whom we must not forget to men- 
tion, was working away very quietly without any help, and 
with very little money; and yet in his way was doing at least 



222 EIGHTEENTH CENTURY. FT. 111. 

as much work as the others. This was William Smith, a 
plain English surveyor, who was so much struck with the 
arrangement of the different formations in the hills among 
which he travelled that he determined to try and map them 
out so as to show exactly how the strata are placed one 
above the other, and what counties they pass through. 

He began his work in 1790, and travelled over the whole 
country, chiefly on foot, marking as he went all the different 
positions of the rocks, and collecting the shells and other 
fossils which he found in them. He had not gone on long 
before he observed that certain fossils which appeared in the 
lower beds disappeared when he reached those which lay 
above them, and that others took their place ; so that in 
this way it was possible to use the fossils to trace out the age 
of any particular rock, just as the face of a coin helps you to 
tell the reign in which it was cast ; and the story told by 
the fossils agreed very well with the divisions which he had 
worked out by the position of the rocks above each other. 
He was even so observant that he distinguished between 
the fossils which had their edges fresh, showing that they 
had not been disturbed since they were buried in the earth, 
and those which were rubbed and water-worn. The fresh 
ones only, he said, are of use to tell the age of a rock, for 
those which are rubbed may have been washed out of some 
older formation by rivers. 

In this way William Smith, for pure love of science, and 
without any hope of gain, travelled over the whole of Eng- 
land and Wales, mapping out the rocks and noticing all 
their peculiarities. In 1799 he published a list or tabular 
view of the formations with their fossils, and the places 
where they might be seen in the hills ; and in 1 8 1 5 he at 
last succeeded in completing a geological map of England, 
which has ever since formed the foundation of our British 



ch. xxvi. WILLIAM SMITH. 223 

geology, and which remains a lasting monument of what one 
man may accomplish by patience and indefatigable industry. 
William Smith fairly earned the title of the ' Father of Eng- 
lish Geologists,' which has ever since been given him, and, 
with Werner and Hutton, deserves to be remembered as one 
of the founders of the science of geology. 



Chief Works consulted. — LyelPs 'Principles of Geology;' LyelPs 
'Student's Elements of Geology;' Page's 'Advanced Text-Book of 
Geology ; ' Hutton's f Theory of the Earth ; ' Fitton's ' Notes on Pro- 
gress of Geology in England $' 'Life of Werner' — 'Naturalists' Library, 5 
vol. xxxix. 



224 EIGHTEENTH CENTURY. 



CHAPTER XXV1T. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

Birth of Modem Chemistry — Black — Bergmann — Cavendish — Priestley 
— Scheele — Rutherford — Lavoisier — French School of Chemistry. 

During the last half of the eighteenth century, while Hunter 
and Linnaeus were adding to our knowledge of living beings, 
and Werner and Hutton were reading the history of the 
crust of the earth, a little group of men in England, France, 
and Sweden were making discoveries which entirely altered 
the science of chemistry. These men were Bergmann and 
Scheele in Sweden ; Black, Cavendish, and Priestley in Eng- 
land ; and Lavoisier in France. 

In order to understand what their discoveries were, and 
what they taught us, it is necessary to bear in mind that up 
to this time chemists had believed air and water to be ele- 
ments or simple substances which could not be decomposed 
or split up into any other kind of matter. Mayow, indeed, 
had shown that the atmosphere could be separated into two 
gases, but his experiments had been passed over and for- 
gotten ; and though Dr. Hales, at the beginning of the 
eighteenth century, had collected several gases, he had not 
distinguished them from air. The fact was that Stahl's 
' phlogiston,' which was supposed to be a substance passing 
out of burning and breathing bodies into the air, was a con- 
stant source of confusion, and led men away from the truth. 



ch. xxvn. BLACK'S FIXED AIR. 225 

But the time had now come when these misty ideas were 
to be dispelled, by the discovery of the four gases — carbonic 
acid, hydrogen, oxygen, and nitrogen. 

Discovery of ' Fixed Air,' or Carbonic Acid, by — 
Black, 1756. — The first step was made by a Scotch 
physician named Black, who was born of Irish and Scotch 
parents at Bordeaux in 1728, and became Professor of 
Chemistry at Glasgow in 1756. Here he made many 
valuable experiments, and among other things he was very 
anxious to find out why limestone altogether changes its 
character when it is burnt. If you take a piece of ordinary 
limestone or chalk, and put it in water, it will remain with- 
out any change unless you add a little acid to the water, 
and then the limestone will effervesce, and bubbles will 
begin to rise up from it. But if you take a piece of the 
same limestone and burn it in a fire, it turns into a powder 
called quick-lime, which will no longer give out bubbles 
when you pour acid upon it, but directly you mix it with 
water it will swell up and become intensely hot, as may be 
seen when bricklayers are making mortar by the roadside. 
This complete change in the limestone, caused by merely 
heating it, had been a great problem to chemists ; and Dr. 
Black was still more puzzled by finding that the lime was 
lighter after it had been burnt, although he could not 
discover that it had lost anything except a little water, 
which was not enough to account for the loss of weight. 

At last he remembered that Dr. Hales had driven air out 
of substances, and collected it in bottles ; and he began to 
consider whether the heat of burning might not have driven 
some heavy kind of air out of the limestone, and so made it 
lighter. To prove this he made the experiment which has 
since been always used for making small quantities of car- 
bonic acid gas. He put some pieces of limestone in the 




226 



EIGHTEENTH CENTURY. 



PT. III. 



bottle, a, Fig. 40, and poured upon them some water and 
some acid. He then stopped the bottle with a tight cork, 
and joined it by the tube b to a large glass jar, c, filled with 
water, and standing with its open end downwards in a 
vessel of water. Immediately bubbles began to rise from 




Fig. 40. 

Carbonic Acid rising from Limestone and Acidulated Water (Griffin); 

a, Bottle containing pieces of limestone in water and acid, b, Connecting tube. 

c, Inverted jar, out of which the rising gas is driving the water. 

the limestone, and passing into the jar, c, drove out the 
water and filled the jar with gas. 

This gas Black called ' fixed air,' because it had been 
fixed in the limestone before it was driven out by the 
acid. He collected and weighed it, and found that it exactly 
made up the weight which the limestoite had lost. He then 
reversed the experiment, and taking some water, which had 
lime dissolved in it, he passed some ' fixed air ' into it, and, 
as he expected, the gas joined itself to the lime and formed 
a powdered white chalk at the bottom of the bottle. By 
these two experiments he proved that limestone and chalk 
are composed of lime and ' fixed air,' and that lime can be 
turned into chalk by causing fixed air to combine with it. 

He then proceeded to examine the gas itself. He found 
that animals died in it, and that a flame would not burn in 



CH. xxvii. CHEMICAL AFFINITY. 227 

it, and also that it was the same gas as that which bubbles 
out of beer and other liquids when they ferment, and often 
out of mineral springs. He also proved that there is * fixed 
air' in our breath. This he showed by breathing into a 
glass of lime-water, and thus forming powdered chalk, 
which fell to the bottom of the glass. 

All this Black discovered about ' carbonic acid,' which 
is sometimes called ' fixed air ' even now, when people speak 
of it in effervescing drinks. He did not know that it is an 
acid ; this discovery was made by Bergmann of Sweden, of 
whom we must now speak. 

Bergmann shows that Fixed Air is an Acid— Works 
out the ' Chemical Affinity ' of many substances. — Tor- 
bern Bergmann, who was born in 1735 in West Gothland, 
was the son of a tax-collector, and he had the greatest diffi- 
culty in getting permission to study science. His parents had 
intended him for the law or the church, and it was not until 
his scientific books had been burnt, and he had fallen ill 
with disappointment, that they saw it was useless to oppose 
him, and he was allowed to take his own course. From 
that time he was happy ; he put himself under the great 
Linnaeus, and in 1761 became Professor of Natural Philo- 
sophy at Upsala, and afterwards of Chemistry at Stockholm. 
Bergmann made a great advance in chemistry by working 
out the ' chemical affinity ' of many substances, and showing 
how to make use of it to test or try mineral waters . 

Nearly a hundred years before Bergmann began to study 
chemistry, Newton, when writing on attraction, had pointed 
out that when substances are mixed together some kinds 
attract each other very strongly and join together, making 
one compound substance. For instance, he said, if you 
put copper into nitric acid the copper will dissolve and dis- 
appear ; but if you plunge a piece of iron into the liquid the 



228 EIGHTEENTH CENTURY. pt. iii. 

copper will re-appear and fall to the bottom of the glass, 
because the iron attracts the nitric acid more strongly than 
the copper does, and so it takes it up out of the liquid, 
setting the copper free. 

Chemists had till now neglected this observation of 
Newton's, but Bergmann followed it out, and by a number 
of experiments he drew up a table of those substances 
which seemed to have the greatest affinity for each other, 
and which would unite whenever the conditions would allow 
them. This he called a table of 'elective affinities.'' 

It is easy to see how this could be used for testing or 
trying what substances lie hidden in mineral waters. Iron, 
for instance, in the case given by Newton, would show when 
copper was dissolved in a liquid containing nitric acid. 
Boyle, too, had shown that a blue liquid extracted from the 
lichen called litmus turns to a bright red directly it touches 
an acid ; so that blue litmus is a sure test of an acid. Again, 
common salt put into a clear liquid containing silver, turns 
it cloudy ; while tincture of gall-nuts makes a purple cloud 
in a solution containing iron. Bergmann worked out a 
number of these tests, and by means of them analysed or 
separated out the substances contained in mineral waters ; 
he even dissolved solid minerals in acids and tested them in 

^ \ the same way. 

v* One of the first uses that he made of his tests was to try 
pQ \ * i>" Black's ' fixed air.' When he heard of this gas he suspected 

<\> that it must be an add, because it joined itself to lime, 
which is an alkali, that is, a substance in all respects unlike 
an acid ; and he had found that unlike substances nearly 
always attract each other most strongly. So he made 
some ' fixed air ' and tested it with blue litmus, and, as the 
litmus turned red directly, he knew that he was right in 
supposing it to be an acid, and he called it ' aerial acid/ or 



>. i^l 



ch. xxvit. HYDROGEN. 229 

acid air. He then weighed it and proved that it was bulk 
for bulk heavier than common air, and by passing it through 
water he showed that a quantity of it would dissolve. 

Thus these two men, Black and Bergmann, had arrived 
at a pretty good knowledge of this gas. They had proved 
that it is an invisible heavy kind of air ; that it dissolves in 
water] that it is acid and joins itself to lime, forming lime- 
stone or chalk; that it destroys life when breathed, and 
puts out a flame ; that it is given out by fermenting liquids, 
and from mineral springs, and is contained in our breath. 
One thing they had not found out, namely, that it is made 
up of two elements ; this was discovered by Lavoisier in 
1779 (see p. 237), when he gave it the name of 'carbonic 
acid.' 

Discovery of Hydrogen by Cavendish, 1766. — The 
next gas discovered was hydrogen, and its discoverer was 
Henry Cavendish, grandson of the Duke of Devonshire, who 
was born in 1731. Cavendish was a very shy and reserved 
man, who lived much alone, and found his greatest pleasure 
in studying science for its own sake. It is even related of 
him that he taught all his servants to understand by signs 
what he wanted in order that he might be able to think 
without interruption. 

In the year 1766 lie read a paper before the Royal 
society upon a gas which he called 'inflammable air/ 
because it burst into a flame whenever a light was brought 
near it, and also because he believed it to be the cause of 
the explosions which so often take place in mines. He 
obtained this gas by pouring sulphuric acid and water upon 
zinc, iron, or tin, and then collecting the bubbles as Black 
had done (see Fig. 40, page 226). But when he began to 
make experiments with this gas he found it very different 
from Black's ' fixed air.' It is true that a candle would not 



^> 



230 EIGHTEENTH CENTURY. pt. in. 

burn, nor could animals live in it ; but when a light was 
brought near it, it took fire and burnt with a pale blue flame 
inside the bottle. Then, instead of being heavy like ' fixed 
air,' it was lighter than the atmosphere, and for this reason 
it was soon used for filling balloons. It had also another 
remarkable peculiarity, that, when mixed with air in a bottle, 
it exploded with a loud noise directly a light was brought 
near it, leaving drops of moisture inside the bottle. Caven- 
dish did not understand the cause of this explosion at first, 
but in 1784 (after Priestley had discovered oxygen) he mixed 
pure oxygen and hydrogen in a closed vessel, and lighted 
them by an electric spark, and then he made the great dis- 
covery that these two gases, when lighted, combine together 
and form water, which is therefore a compound substance 
made of oxygen and hydrogen. 

Oxygen discovered by Priestley in 1774, and by 
Scheele in 1775. — The next gas discovered was oxygen, 
the most common and the most useful of all the substances 
in our globe. It was discovered independently by two men 
— Priestley, a dissenting minister at Leeds, and Scheele 
(born 1742), a small apothecary at Kjoping, a little village 
in Sweden. 

There is no doubt that Scheele deserves as much credit 
for this discovery as if Priestley had never made it, for he had 
not heard of his experiments, and he added many useful 
facts which Priestley did not know. Still, as they both went 
over much the same ground, we cannot afford space here to 
give Scheele's experiments. You must not, however, forget 
his claim, for though the world often forgot him because he 
remained a poor apothecary all his life, yet ^k^p was 
really one of the first chemists of Europe. We owe to him 
the di scovery of ejbtoine ; an dof mangane se, baryta, fluoric 
acid, and many other substances whose names I cannot 



ch. xxvii. OXYGEN. 231 

expect you to know. Indeed, his merit was so great that 
Bergmann, his friend and patron, once said, ' The greatest 
discovery he ever made was when he discovered Scheelc' 

Joseph Priestley, the discoverer of oxygen, was born in 
1733. The greater part of his life was spent in writing upon 
religious subjects, and it was only in his leisure hours that 
he studied chemistry. He tells us in his autobiography that 
he first began to take an interest in such things in conse- 
quence of visiting a brewery next door to his house and 
watching the fixed air which rose from the beer-vats. His 
first chemical experiment of any value was to force this 'fixed 
air ' into pure water, thus making an effervescing drink, much 
the same as the soda-water we drink now. He next tried 
what effect growing plants have upon air, and by keeping a 
pot of mint u^der a bell-jar in which the air had been spoilt ^y* „*/f 




y 



by burning or breathing, he proved that plants take up the y\ t 
bad air and render the remainder fit again to support a 
flame or life. He did not, however, yet know why this took 
place. He also invented a number of troughs and other 
apparatus for collecting and washing gases, and amused 
himself as Hales had done in driving gas out of different 
substances. 

And thus it happened that one day, August 1, 1774, he 
made an experiment which led to a great discovery. He 
took a red powder called mercimc oxide, which he knew 
contained mercury and something else besides, and he put 
it into the bulb, a, Fig. 41 ; the rest of the tube he filled 
with mercury, and passed it into the basin b, and up 
into the jar r, both b and c being also filled with mercury. 
He next took a powerful burning-glass, d, and brought the 
rays of the sun to a focus upon the red powder. As soon 
as the powder became very hot a gas rose out of it and 
passed along the tube into the jar, c, driving out the mer- 



232 



EIGHTEENTH CENTURY. 



cury ; while the red colour began to disappear in the bulb, 
a, and only pure shining mercury remained behind. So far 




Fig. 41. 

Priestley's Apparatus for procuring Oxygen. 

a, Bulb containing red mercuric oxide, b, Vessel containing mercury, c, Inverted 

jar for collecting the gas. d, Burning glass. 

he had only proved that red mercuric oxide is made up of 
mercury and a gas. 

When he had collected enough gas to experiment upon 
he passed some of it through water, and found that it did not 
dissolve as ' fixed air ' does ; but what surprised him still 
more was that a candle put into it burnt with a large 
vigorous flame, and a piece of red-hot charcoal burnt 
in it furiously. It was clear, then, that this could not 
be either ' fixed air ' or ' inflammable air,' for neither 
of these would feed a flame. He next put two mice into 
some of the gas, and he found that they lived much 
longer than they would have done in the same amount of 
ordinary air. When he breathed it also into his own chest 
he felt singularly light and easy for some time afterwards. • 
' Who can tell,' he writes, ' whether this pure air may not 
at last become a fashionable luxury? As yet only two 
mice and myself have had the privilege of breathing it.' 



ch. xxvii. PRIESTLEY'S DISCOVERIES. 233 

Here, you see, we have come back again to Mayow's 
fii-e-air, so long forgotten, which supports life and flame. 
Priestley had learnt more about it than Mayow had, for he 
had collected it separately, had shown that it is the gas 
which supports combustion, and had breathed it without 
other air being mixed with it ; moreover, he had shown that 
it could be driven out of metallic compounds, for mercury 
is a metal. Yet it is disappointing to learn that, in spite 
of having gone thus far, Priestley was so imbued with Stahl's 
theory of ' phlogiston,' that he did not really understand 
the great discovery he had made, but called his gas 
■ dephlogisticated air,' or air which had lost that imaginary 
' phlogiston ' which was always confusing men's minds. 

There is no doubt that he discovered the gas and showed 
that it was the chief actor in combustion and respiration, 
and for this discovery and that of other gases, he was 
elected a member both of the Royal Society and of the 
Academie des Sciences, and his fame was great all over 
Europe ; yet still he had not hit upon the entire truth — 
he had given the facts, and it remained for Lavoisier to 
read the riddle. 

Besides his chemical writings, Priestley .published many 
books on theology, and though he was a singularly gentle 
quiet man, yet his religious and political essays were often 
very severe, and they led to his being driven out of Bir- 
mingham, and his house burnt by the mob, when they 
attacked the leading Dissenters during the panic caused by 
the French Revolution. After living for some time near 
London he emigrated to America, where he died in 1804. 
He continued his chemical experiments up to the time of 
his death, and made many important discoveries, but the 
chief discovery which will always be connected with his 
name was that of oxygen, in 1774. 




234 EIGHTEENTH CENTURY. ft. hi. 

Properties of Nitrogen determined by Dr. Ruther- 
ford in 1772. — There now remains to be mentioned only- 
one of the four gases spoken of at page 225, namely, nitrogen. 
This gas was first properly described by Dr. Rutherford in 
1772, but there is very little to be said of it except that it 
has scarcely any of those properties which belong to the 
other gases. It does not support life or flame like oxygen ; 
it does not make lime-water cloudy as carbonic acid does, 
nor does it burn like hydrogen. In fact, it is a dull sleepy 
gas, which remains after oxygen has been taken out of the 
air. 

Lavoisier lays the Foundation of Modern Chemistry, 
1778. — The determination of nitrogen completes the history 
of the discovery of those gases which play the chief part 
in combustion, respiration, and the maintenance of animal 
and vegetable life. But you will have noticed that we 
have not yet arrived at the new explanation of chemical 
changes which was to take the place of 'phlogiston.' 
The fact is that Bergmann, Cavendish, Scheele, and 
Priestley, were all so cramped by the old theory, that 
though they discovered the facts they could not make the 
right use of them. Black had, indeed, proved that fixed 
air would combine with lime (see p. 227), but he did not 
work out any theory of combustion from this discovery. 
The man who did this, and who laid the foundation of 
modern chemistry, was the celebrated French chemist, 
Lavoisier. 1 

1 This statement having been questioned by one of the reviewers of 
the first edition of this book, it may be well to quote the words of Dr. 
Crum-Brown, upon whose advocacy of Black's claims to precedence 
the objection was founded. After stating how Black 'was the first to 
point out the new path,' Dr. Brown continues, ' We would be ungrate- 
ful if we undervalued the services of the French chemist. The facts 



ch. xxvii. LA VOISIEtfS EXPERIMENTS. 235 

Antoine Laurent Lavoisier was born in Paris in 1743. 
His father, who was a wealthy merchant, gave him a 
splendid education, and when he was still quite young the 
new discoveries which were being made in chemistry tempted 
him to learn that science. At twenty-one years of age he 
received a gold medal from the Academie des Sciences for 
a very elaborate and learned essay on the best way of light- 
ing the streets of Paris. At five-and-twenty he was elected 
a member of the Academie, and from that time he deter- 
mined to devote his life to chemistry. 

As early as 1770 Lavoisier had begun to suspect that 
the famous theory of phlogiston was false. His chief reason 
for thinking this was that he found, as Geber had done more 
than 900 years before (see p. 44), that when metals are 
heated so that they turn into powder, the powder weighs 
more than the original metal did before it was heated. 
Moreover, he also found that the air which remained behind 
in the vessel in which the metal had been heated had lost 
exactly as much weight. as the metal had gained. So it seemed 
to him clear that the metal must have taken something/hwz 
the air instead of giving anything to it. 

For eight years Lavoisier worked incessantly at this 
problem. He heated many metals, such as iron, lead, tin, 
etc., and other substances such as sulphur and phosphorus, 
and in every case, if he collected all that remained, he found 
it heavier than before. But there was one point in which he 
could not succeed j he could not make the metals give back 
again what they had taken from the air, so that he might 
examine it At last, in 1778, it occurred to him that 
Priestley had separated mercuric oxide into two substances ; 

discovered by Priestley, Scheele, and Cavendish, were merely the raw 
material out of which Lavoisier constructed a consistent and comprehen- 
sive theory.' Inaugural Lecture, Edinburgh, 1869. 

12 



236 EIGHTEENTH CENTURY. pt. hi. 

namely, the metal mercury and a gas. Here, then, was just 
the step he wanted. If he could first make mercuric oxide 
by heating mercury in the air, and then afterwards separate 
it back again into mercury and a gas, he would thus prove 
what it had taken out of the air. He therefore took some 
mercury and put it into a tube a, Fig. 42, which was connected 




Fig. 42. 

Lavoisier's Apparatus for Heating Mercury and making it take up Oxygen. 

A, Bulb containing mercury, b, Vessel containing mercury, c, Bell-jar partly full 

of air. d, Stove. 

with a bell-jar c, containing air and standing over mercury. 
Then he heated the bulb a over the stove d, and kept the 
mercury boiling for twelve days. 

During the first five days little by little red specks began 
to appear on the top of the mercury in c, that is, mercuric 
oxide was fonned ; but after that time, when about one-fifth 
of the air in the bell-jar, c, had disappeared and mercury 
risen in its place, no further change took place. He then 
lifted off the bell-jar and took 45 grains of this red powder 
and made Priestley's experiment with it (see p. 232), and 
he obtained, of course, the gas which Priestley had called 
1 dephlogisticated air/ He afterwards found by more exact 
experiments that the amount of this gas contained in the 
mercuric oxide exactly equalled the amount lost by the air 
in which the mercury had been heated. 



ch. xxvil. LA VOISIER'S EXPERIMENTS. 237 

Now see what Lavoisier had done : he had proved that 
the reason why air shrinks when substances are burnt in it, 
is because the substances take up a gas out of the air, and he 
had also shown that this gas is the same as that which ' 
Priestley discovered. Now, at last, the false theory was 
destroyed, and the starting-point of a true theory was found. 
The imaginary phlogiston, which had been supposed to load 
the air when anything was burnt in it, was proved never to J 
have had any existence ; for it was clear that just the I 
opposite effect takes place. All burning and breathing and 
the change in metals is caused by a gas being taken up out j 
of the air and joined to other substances. Lavoisier called 
this gas oxygen (from dgvs, acid ; yeiWw, I produce), because 
he found that most substances were acid after they had 
been united with it This, too, led him to suspect that as 
' fixed air ' was an acid, and could be made by burning char- JUr^* - 

coal, it must be composed of oxygen and carbon. So he (s ^ 
burnt small quantities of charcoal in pure oxygen, and by ^ 
analysing the 'fixed air' produced proved that 100 parts by 
weight of this gas contained 72 parts of oxygen and 28 of 
carbon. For this reason he called it 'carbonic acid,' a 
name which it still bears. By burning a diamond in oxygen 
and producing carbonic acid, he also proved that a diamond 
is pure carbon. 

Lavoisier had very great difficulty in persuading the 
other leading chemists that they had been labouring under 
a false idea, and that substances when burning do not put 
something into the atmosphere but take a gas out of it. Dr. 
Black was one of the first to teach the new theory, 
as was natural, since he had led the way to it by the 
experiments he had made with 'fixed air,' but Priestley 
died without giving up his old opinions. The younger 
chemists, however, saw the truth of Lavoisier's explana- 







238 EIGHTEENTH CENTURY. PT. in. 

tion, and from this time chemistry advanced very rapidly. 
Lavoisier invented an entirely new set of terms instead 
j](r j* of the old names of the alchemists, and though his 
'terms have been greatly altered by later discoveries, still 
many of them will always be used. He repeated with a 
jT better apparatus Cavendish's experiment of turning hydrogen 
v r\(\ / and oxygen into water, and he gave hydrogen its name from 
(T-f ^ry ^cd/>, water, and yevvdu, I produce. Lastly, he published 
'Vi i his l Elements of Chemistry,' in which he gave a clear 
y / explanation of the different chemical changes, and how 
(y students could work them out for themselves. 

Lavoisier was now at the height of his fame, full of his 
new theory, and prepared to devote the rest of his life to 
making chemistry a grand science ; but a very sad fate was 
awaiting him. In 1793 the great French Revolution broke 
out in Paris. Lavoisier was a farmer-general, that is a kind 
of collector of taxes, and all the farmers-general were hated 
by the people ; so he knew that he should most likely lose 
all his fortune, and was prepared to work for his living ; but 
he had not expected the blow which fell upon him. All the 
farmers -general were condemned to death, and though a 
physician named Halle, who deserves always to be remem- 
bered for this act, pleaded that Lavoisier's life should be 
spared till he had completed his experiments, the ignorant 
and brutal Government replied, ' We do not need learned 
men,' and on May 18, 1794, at the age of fifty-one, Lavoisier 
was guillotined. 

After his death the French School of Chemistry, took the 
lead for many years, until new discoveries in England, which 
we shall mention by and by, made another great advance. 
* When you are able to read larger works upon the history of 

chemistry you will find how very interesting the period was 
of which we have been speaking. I have only been able to 



ch. xxvii. RAPID ADVANCE OF CHEMISTRY. 239 

give you here the very barest outline of it, so that the names 
of these great chemists may not be quite unfamiliar when 
you meet with them in other books. 



Chief Works con stilted. — 'Three Papers on Factitious Air,' by 
Cavendish — 'Phil. Trans.,' 1766; Brande's 'Chemistry;' Hoefer's 
' Histoire de la Chimie ; ' Cuvier, 'Histoire des Sciences Naturelles;' 
Huxley, ' On Priestley ' — 'Macmillan's Magazine,' 1874; Priestley, 'On 
Different Kinds of Air,' 1774; Thomson's 'Hist, of Royal Society j' 
Scheele's 'Chemical Experiments on Air and Fire,' translated 1 780; 
Miller's 'Elements of Chemistry 5' Lavoisier's 'Elements of Chemis- 
try,' translated by Kerr, 1790. 



240 EIGHTEENTH CENTURY. ft. ill. 



CHAPTER XXVIII. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

Dr. Black on Latent Heat — Watt's Application of the Theory to the 
Steam-engine — Early Histoiy of Steam-engines — Newcomen's 
Engine — Watt's Engine — Watt and Boulton. 

Discovery of Latent Heat by Dr. Black in 1760. — We 

must now go back a few years, to the time when Dr. Black 
was lecturing at Glasgow in 1760; for he then made a 
remarkable discovery about heat, which belongs to the 
history of physics rather than of chemistry. This was the 
discovery of latent heat, or of heat which becomes lost or 
hidden whenever a solid is turned into a liquid, or a liquid 
into a gas. 

If you put a lump of ice in a saucepan on a stove, and 
when it begins to melt stir it gently so as to keep the water 
well mixed, you will find that so long as the smallest piece of 
ice is left in the water, a thermometer standing in the sauce- 
pan will not rise higher than o° Centigrade, or the melting- 
point of ice. Now the heat from the stove must be con- 
tinually entering the water, otherwise the ice would not melt. 
What then becomes of this heat? Again, if you keep the 
water on the stove after the ice is melted, it will grow hotter 
and hotter till it reaches ioo° Centigrade, when it will boiL 
Here, again, it will remain at the same temperature, and 
though you go on boiling it till it has all passed away in steam, 
the last drop of water will never be hotter than ioo° C. So 



ch. xxviii. LATENT HEAT, 241 

that here again the heat which is added remains hidden 
and does not became apparent. This last fact about boil- 
ing water had been long known to philosophers, but no 
one found any explanation of it until Black began his ex- 
periments on melting ice ; and he then came to the conclu- 
sion that the heat is employed in altering the condition of 
the water, that is, in changing it, in the one case from solid 
ice into water, and in the other from water into a vapour. 

He proved this by some simple experiments which are 
not difficult to make. He took two glass flasks, and filled 
one with ice just on the point of melting, and the other 
with an equal weight of ice-cold water. These he hung in 
a moderately warm room, which he kept all the time at the 
same heat (8°*5 C). At the end of half an hour the ice- 
cold water had risen four degrees (from o° to 4 ), but the 
melting ice remained at o°, and it was ten hours and a half 
before the ice had disappeared, and the water had reached 
the same temperature as that which the water in the other 
basin had attained in half an hour. Now the melting ice 
had been receiving heat for twenty-one half- hours, and 
therefore had taken in 2 1 x 4, or 84 of heat, while it only 
showed a rise of 4 . It was clear, therefore, that the re- 
maining 8o° must have been spent in turning the ice into 
water. 

Black now tried the same thing in another way. He 
found that a pound of water at 79 C. would • exactly melt 
a pound of ice. So he again took two vessels, in one of 
which he put a pound of ice-cold water at o°, and a pound 
of hot water at 7 9 , and when they were properly mixed he 
found, as he expected, that the heat of the mixture was 
half-way between the two, that is 39J . In the other 
vessel he put a pound of ice at o°, and a pound of hot 
water at 79 , and here, when the ice had disappeared, the 



242 EIGHTEENTH CENTURY. pt. in. 

mixture still remained at o°, showing that the whole 79 of 
heat in the boiling water had been absorbed in melting the 
ice, and remained hidden or latent in the two pounds of 
water. The latent heat of water is therefore between 79 
and 8o°. 

We know now what becomes of this heat, as you will 
see (Chapter XXXV.) in the history of the science of the 
nineteenth century ; but the first step was to prove its dis- 
appearance into the water, and this we owe to Black ; as 
well as the fact that still more heat is lost in turning water 
into steam. 

This last fact he proved by filling a glass bottle half full 
of water, corking it very tightly, and then heating the bottle 
till the water began to boil. He was obliged to do this 
very gently, because the outward pressure of steam increases 
very rapidly as the temperature rises, and he did not wish 
to drive out the cork or break his bottle. After a little 
time the water ceased boiling, because the other half of the 
bottle was full of steam, and there was no room for more 
to form. But now the water began to grow hotter and 
hotter, and rose above ioo° C, showing that when the 
heat could no longer form steam it did not remain hidden, 
but increased the temperature of the water. At last, when 
he was afraid to heat the bottle any more, he loosened the 
cork, which flew out with great violence, followed by a 
cloud of steam. And now notice what happened ; directly 
the rush of steam was over, the heat of the water in the 
bottle fell again to ioo° C, for all the rest of the heat had 
been used in forming more steam the moment the pressure 
was removed. 

James Watt, 1736-1819. — Black had now completed 
his discovery, and from that time he taught in all his 
lectures that heat becomes latent or absorbed when a solid 



CH. xxviii. JAMES WATT, 243 

is changed into a liquid, or a liquid into vapour. It was 
about this time that the famous engineer, James Watt, began 
to study the power of steam, and as Black was his friend, 
he came to him to help him solve his difficulties. The 
history of the steam-engine, being the history of an inven- 
tion, does not strictly belong to our work; but the use 
which Watt made of the discoveries about steam is a part 
of science, and we must therefore find room for a slight 
sketch of it here. 

James Watt was born at Greenock in 1736 ; he was the 
son of a builder and shipwright, and was so delicate as a 
child that he was kept at home, and learnt reading from 
his mother, and writing and arithmetic from his father. 
When at last he was sent to school he found it hard work, 
for he was slow and thoughtful, and the other children jeered 
at him for his want of quickness. Every one knows the 
story of his being scolded by his aunt for sitting silent a 
whole hour, holding first a spoon and then a saucer over 
the steam rising from a kettle, and watching the drops of 
water gathering upon them. It was in this quiet way that 
little James's mind grew, and it may be an encouragement 
to slow, plodding boys to know that one of our greatest in- 
ventors was considered a dull and backward child. 

As he grew older James went up to London, and there, 
after overcoming many obstacles, which the guilds, or trades' 
unions of those days, put in the way of all independent 
workers, he learnt to make mathematical instruments, 
and then returned to Glasgow, where he began business. 
Though he was only one-and-twenty he soon became known 
as a man of unusual ability, for the mind of the dull boy 
had developed, and his thoughtfulness had begun to produce 
results. Not only the students, but even the professors of 
the University used to stroll into his little shop to discuss 



244 EIGHTEENTH CENTURY. VT. ill. 

the discoveries of the day. ' Whenever any difficulty ar- 
rested us,' writes a student named Robison, ' we used to run 
to our workman, and he never let go his hold until he had 
entirely cleared up the proposed question.' One day it was 
necessary to read a German book on mechanics ; Watt 
immediately set to work and learnt German, and another 
time, for the same reason, he studied the Italian language. 
It is scarcely surprising that a man with such talent and 
perseverance as this, who was also gentle and loving to 
everybody, should be sought after both by masters and 
students. 

Among those who came to Watt's shop was one Ander- 
son, professor of physics, who, finding that a little model of 
a steam-engine in the University museum was out of order, 
brought it to Watt to be repaired, and thus led the way to 
his invention. And here it is necessary to point out two 
things : First, you must not suppose that by a steam-engine 
is meant a railway engine ; all contrivances which move by 
the power of steam are steam-engines, and locomotive engines 
which draw carriages were not made till 1804, long after 
Watt's time. Secondly, you must get rid of the idea, which 
many people have, that Watt was the first man to make an 
engine which moved by steam. This was done long before 
his time. The thing which Watt really did was to make 
an engine such as we now use, working entirely by steam, 
without the help of air, and doing an enormously greater 
amount of work with the same quantity of fuel than any 
others had done before. 

The Newcomen Engine, 1705. — Steam had been 
used to turn a globe by Hero of Alexandria, a Greek who 
lived 120 years before Christ; and Baptiste Porta in 1580, 
Solomon de Caus in 16 15, and the Marquis of Worcester 
in 1663, all tried to make use of steam to do work. Again, 



CH. XXVIII. 



NEWCOMERS ENGINE. 



245 



in 1690 and 1698, a Frenchman named Papin and an 
Englishman, Captain Savery, tried to make steam-engines 
to raise water out of mines. But the only one of all these 
engines which we need describe here was that which fell 




Fig. 43. 

Newcomen Engine (Black). 

a, Stopcock between boiler and cylinder, b, Stopcock between cold-water tank and 
cylinder, c, Valve closing air-vent, d, Valve closing the outlet for condensed 
steam, e, Weight which drags down the beam, fi, p, Piston which is pressed 
down by the atmosphere when the cylinder is empty. 1 

into the hands of Watt, and which was made by a man 
named Newcomen in 1705. A section of Newcomen's 
engine is given in Fig. 43. Its working depended on the 
pressure of the atmosphere (explained p. 120) on the piston 

1 The boiler and cold-water tank both in this Figure and in Fig. 45 
are drawn much too small in proportion, in order to bring them into 
the Figure. 



246 EIGHTEENTH CENTURY. pt. hi. 

at one end of the beam, and the weight of the lump of 
iron, e, at the other end. 

The lever-beam of this engine is balanced in such a 
way that when it is not at work the weight e pulls it down 
on the side away from the engine, and the piston, p, p, is 
drawn up to the top of the cylinder, as in the figure. To 
set the engine going a fire is lighted under the boiler, and 
the tap or stopcock, a, is opened, so that the steam rises 
into the cylinder, driving out the air through the air-vent, c. 
As soon as the cylinder is full of steam, a is turned off, and 
the stopcock, b, turned on. Immediately a small jet of 
cold water from the tank t rushes through b into the cylin- 
der, turning the steam back into a few drops of water, 
which flow out with the cold water down the pipe d. Now 
notice, the cylinder is quite e?npty; for the steam drove out 
the air, and the cold water carried the steam away with it, 
while no air can come in at c or d, because the little valves 
in them are kept shut by the weight of the atmosphere out- 
side. So there is nothing to hold up the piston, which is 
being heavily pressed down by the air above it. The con- 
sequence is, down it comes to the bottom of the cylinder, 
dragging with it the end of the lever-beam. Directly it 
reaches the bottom the stopcock b has to be shut, and a 
opened again. Up rises the steam directly from the boiler, 
driving up the piston, and the whole thing begins again. In 
this way the lever-beam is kept moving up and down by 
simply turning the two stopcocks one after the other. These 
were at first opened and shut by boys ; but one day an in- 
genious lad named Humphrey Potter, who wanted to save 
himself the trouble of turning the cocks, found that by 
tying strings from the handles to the different ends of the 
beam he could make the engine open its own cocks as the 
beam went up and down. This rough arrangement was 
scon improved, and the machine worked by itself. 



ch. xxviii. CONDENSATION OF STEAM. 247 

"Watt's Separate Condenser. — Such was the engine as 
Watt found it. When he began to examine it, he saw at 
once what an immense quantity of heat was wasted. Every 
time the piston came down, the cylinder, as well as the 
steam in it, had to be cooled down ; every time the piston 
rose, the cylinder had to be heated again ; and the thing 
which puzzled him most about it was, that it took six pounds 
of cold water to condense only one pound of steam. 

It was in this difficulty that he came to Dr. Black, and 
learnt from him the theory of latent heat, which showed that 
there is an immense store of heat hidden in steam, which 
has to be drawn out before it can become water. This was 
an entirely new light to Watt, and it led him to make many 
experiments still more exact than those of Dr. Black, which 
convinced him that no engine would ever work well or 
economically, while so much power was wasted in cooling 
and re-heating the cylinder at every stroke. But how was 
he to cool down the steam without cooling the cylinder 
which held it? 

For months he pondered over this without finding any 
answer. At last, one Sunday afternoon, when he was walk- 
ing on the Green of Glasgow, the way to do it flashed upon 
his mind. If he could draw the steam off into a separate vessel 
and condense it there, the cylinder might still be kept hot, and 
the thing would be done. Fig. 44 will help you to understand 
how this could be effected. Here the two flasks, a and 
b, are first quite emptied of air, and b is half filled with 
water. Under b is placed a lamp, d ; under a, a basin of 
ice, e. Now as long as the tap, c, is kept open, the steam 
which is constantly rising from the water in b will rush along 
the tube into the empty flask, a, and will there be turned 
into drops of water by the cold of the ice underneath, and 
this will go on as long as there is any water left in b, 



248 EIGHTEENTH CENTURY. ft. hi. 

because there will always be an empty space or vacuum in 
a to receive the steam as it rises. When the tap, c, is shut, 
the steam in b will become very dense, and when it is 
opened again, the greater part of the steam will rush out and 
be cooled down in a, while b remains hot as before. 




Fig. 44. 

Steam condensed in a separate vessel. 

A, Flask empty of air. b, Flask half-full of water and empty of air. c, Tap con- 
necting the two bottles, d, Spirit-lamp keeping the water in b boiling, e, Basin 
of ice cooling down the steam which passes into a. 

Watt's Engine. — This was exactly the plan Watt 
adopted in his steam-engine ; b answers to his cylinder 
(Fig. 45), which could be kept always hot, and a to his 
condenser, in which his steam was turned back into water. 
We cannot follow out all the different steps of his inven- 
tion, and must content ourselves with a rough description 
of his engine after he had completed it, as shown in Fig. 45. 

In the first place you must notice that cold water is 
kept flowing down from the tank a into b, and out through 
the pipe c, so that the condenser standing inside B is kept 
quite cold; and, secondly, I must tell you that the rods, 1 and 
2, are so placed that when the engine-end of the lever-beam 
is raised, as in the figure, the stopcocks a and c are open, 
and b and d are shut ; and when that end of the beam falls, 
b and d will be open, and a and c will be shut. 



ch. xxvin. 



WATT'S ENGINE. 



249 



Let us now begin with the machine as we see it in the 
figure. In this position of the beam the cocks a and c are 
open ; therefore, the steam below the piston will rush out 
at c into the condenser, there to be turned into drops of 

A 

COLD WATER 




a, b, Cold water tanks, c, Outlet for cold water, d, e, Pumps for drawing off hot 
water and sending it along s, s, back to the boiler, p, Tight - fitting piston. 
a, d, Cocks for letting steam into the cylinder, b, c, Cocks for letting steam out 
of the cylinder, e, e, Pipe which carries steam from boiler to cylinder. 0, o, Pipe 
which carries steam from cylinder to condenser. 1, 2, Rods connecting the cocks 
with the lever-beam. 

water, while the steam from the boiler, entering at a, will 
force the piston down. But now, the piston having pulled 
down the beam, a and c will be closed and the other two 
cocks, b and d, will be opened. So the steam above the 
piston will rush out at b into the condenser, while the steam 



250 EIGHTEENTH CENTURY. pt. hi. 



from the boiler will pass directly from e down to d, and 
coming in below the piston, will drive it up again. In this 
way, although the cylinder is never cooled, the piston 
moves steadily up and down ; because the steam is driven 
off into the condenser standing in b, where it is turned 
into water, and is drawn up by the two pumps d and e, 
and sent along the pipe, s, s, back to the boiler. 

This was the principle of Watfs double-acting steam- 
engine, and if you understand the difference between Figs. 
43 and 45, you will see that though Watt was not the first 
to make engines move by steam, he was the first to make 
a pure steam-engi7ie, where the piston moves up and down 
without any help from the outside air, or of the counter- 
balancing weight e, Fig. 43, and without the enormous 
waste of heat and fuel which made all the earlier engines 
comparatively useless. 

I have only attempted to explain the way in which he 
applied steam to his engines ; all the numberless other 
improvements which he made must be studied in books on 
engineering. For twenty long years he went on improving 
and inventing without reaping any reward for his labour. 
Other men tried to steal his ideas and to make a profit out 
of his genius, and he had to fight against prejudice and 
injustice, and against constant depression caused by his 
own ill-health. Yet he found many kind friends upon his 
road, and amongst the most famous of these was Boulton, 
the Birmingham manufacturer, who became his partner in 
1769, and stood by him manfully in all his difficulties and 
troubles. It was from Boulton's manufactory at Soho (a 
suburb of Birmingham) that "Watt's engines went forth to 
the world, and worked that great change in the manu- 
factories of England which has made us one of the first 
nations of the world. 



ch. xxviii. BOULTON AND WATT, 251 

The names of Boulton and Watt deserve to be classed 
together as benefactors of mankind. Watt was the inventor, 
the man who loved science, and who could not live without 
creating. Boulton was the large-minded, enterprising man 
of business ; he gave Watt men, money, courage, and sup- 
port to carry out his inventions ; and by his sympathy with, 
and command over, the workmen, he led the army which 
conquered indifference, persecution, and difficulties, and 
established steam machinery in all the workshops of the 
world. Watt died in 18 19, in the eighty-third year of his 
age, and was buried in Handsworth Church, near his friend 
and partner Boulton, who had died ten years before. 



Chief Works consulted. — Black's 'Elements of Chemistry,' 1803; 
'Edinburgh Review,' vol. xiii. 'History of Steam Engines;' 'Arago, 
Biographies of Scientific Men,' 1857 ; Smiles's 'Lives of Boulton and 
Watt;' Everett's Deschanel's 'Natural Philosophy;' TyndalPs 'Natural 
Philosophy;' Balfour Stewart's 'Treatise on Heat;' Beckmann's 'His- 
tory of Inventions.' 



252 EIGHTEENTH CENTURY. pt, ill. 



CHAPTER XXIX. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

Benjamin Franklin, born 1706 — His Early Life — Du Faye discovers 
two kinds of Electricity — Franklin proves that Electricity exists in 
all bodies, and is only developed by Friction — Positive and Nega- 
tive Electricity — Franklin draws down Electricity from the Sky — 
Invents Lightning-conductors — Discovery of Animal Electricity by 
Galvani — Controversy between Galvani and Volta — Volta proves 
that Electricity can be produced by the Contact of two Metals — 
Electrical Batteries — The Crown of Cups — The Voltaic Pile. 

Benjamin Franklin, born 1706.— He Investigates the 
Nature of Electricity, 1746. — Benjamin Franklin, the 
printer and man of science, was born at Boston, in America, 
in the year 1706. He was the son of a tallow-chandler, 
and had so many hard struggles in his early life that 
he does not seem to have turned his thoughts to science till 
he was nearly forty years of age. His father intended 
him for the Church, but there was not enough money to 
pay for his education, so he was apprenticed to his brother, 
who was a printer. Here he worked very hard, yet he used 
to snatch every spare moment to read any books which 
came within his reach ; but his brother being unkind and 
harsh to him, a quarrel sprang up between them, and Ben- 
jamin at last ran away to New York, and from there to 
Philadelphia. In this last place he got a little work, but 
hoping to do better in England, he came to London, where 



ch. xxix. BENJAMIN FRANKLIN. 253 

he learnt many of the newest improvements in printing. 
After a time he went back to Philadelphia, and from that 
time he began to succeed as a printer, and became a well- 
known and respected man. 

It was in the year 1746 that he first began to pay atten- 
tion to the experiments in electricity which were being made 
in England and France. A great deal had been learnt 
about this science since the time when Otto Guericke made 
the first electrical machine in 1672, and a Frenchman 
named Du Faye had shown that two different kinds of 
electricity could be produced by rubbing different ,, sub- 
stances. You will remember that a pith-ball, when charged 
with electricity from a stick of electrified sealing-wax, draws 
back, and will not approach the sealing-wax again (see p. 
122). But Du Faye discovered that if you rub the end of 
a glass rod with silk, and bring it near to this ball, it will 
draw the ball towards itself, showing that the electricity in 
the glass rod has exactly the opposite effect to that in the 
sealing-wax. In other words, while Guericke had shown 
that substances charged with the same kind of electricity 
repel each other, Du Faye showed that substances charged 
with different kinds of electricity attract each other. Both 
these men thought that electricity was a fluid which was 
created by the rubbing, and which was not in bodies at 
other times; when Franklin, however, began to make his 
experiments, he came to the conclusion that this was not as 
they had supposed, but that all bodies have more or less 
electricity in them, which the rubbing only brings out. 

The way in which he proved this is very interesting ; 
but to understand it you must first know that any body 
which is to be electrified requires to be so placed that the 
electricity cannot pass away from it into the earth. The 
best way to do this is to place it upon a stool with glass 



254 EIGHTEENTH CENTURY. ft. iil 

legs, because electricity does not pass easily along glass. 
You must also know that when any substance is charged 
with electricity, if you bring your finger or a piece of metal 
near to it, a spark will pass between the electrified sub- 
stance and your finger or the metal. 

You will now, I think, be able to follow Franklin's 
experiments. He put a person, whom we will call a, upon 
a glass stool, and made him rub the glass cylinder of an 
electrical machine with one hand and place his other hand 
upon it to receive the electricity. Now, he said, if elec- 
tricity is created by the rubbing, this person must be filled 
with it, for he will be constantly taking it from the machine, 
and it cannot pass away, because of the glass legs under the 
stool. But he found that a had no more electricity in him 
after rubbing the cylinder than he had before, neither could 
any sparks be drawn out of him. He then took two 
people, a and b, and placing each of them on a glass stool, 
made a rub the cylinder, and b touch it, so as to receive 
the electricity. Now notice carefully what happened, b was 
soon so full of electricity that when Franklin touched him, 
sparks came out at all points ; but what was still more curious, 
when Franklin went to a and touched him, sparks came out 
between them just as they had done between him and b. 

This he explained as follows : ' a, b, and myself,' he said, 
* have all our natural quantity of electricity. Now when a 
rubbed the tube, he gave up some of his electricity to it, 
and this b took, so that a had lost half his electricity and b 
had more than his share. I then touched B, and his extra 
charge of electricity passed into me and ran away into the 
earth. I now went to a, and I had more electricity in me 
than he had, because he had lost half his natural quantity, 
and so part of my electricity passed into him, producing 
the sparks as before.' 



ch. xxix. EXPERIMENTS IN ELECTRICITY. 255 

This Franklin believed to be the case with all electricity, 
namely, that every body contains its own amount of it, but \ 
that when for any reason it is distributed unequally, those I 
which have no more than they can well carry, give some up 
to those which have less, till they have each their right 
quantity. And this explained at once why a man cannot 
electrify himself, for so long as he has no one else from 
whom he can procure electricity, he is only taking back with 
one hand what he gives out with the other. Those who 
had too much electricity were called by Franklin positively 
electrified, and those who had too little, negatively electrified, 
but the terms positive and negative are now used differently, 
the one for vitreous the other for resinous electricity. 

Franklin draws down Lightning from the Sky. — It 
was in 1749, when he had already made most of his experi- 
ments upon electricity, that Dr. Franklin began to consider 
how many of the effects of thunder and lightning were the 
same as those which he could produce with his electrical 
machines. Lightning travels in a zigzag line, said he, and 
so does an electric spark ; electricity sets things on fire, so 
does lightning ; electricity melts metals, so does lightning. 
Animals can be killed by both, and both cause blindness ; 
electricity always finds its way along the best conductor, or 
the substance which carries it most easily, so does lightning ; 
pointed bodies attract the electric spark, and in the same 
way lightning strikes spires, and trees, and mountain tops. 
Is it not most likely that lightning is nothing more than 
electricity passing from one cloud to another just as an 
electric spark passes from one substance to another ? 

Franklin communicated these ideas to the Royal Society 
in London, suggesting at the same time that, if he was right, 
it would be possible to prevent a great deal of the harm 
done by lightning by fixing upright rods of iron near high 



256 EIGHTEENTH CENTURY. pt. hi. 

buildings so that the electricity might run down from the 
clouds into the earth without doing any harm. But this 
notion seemed so absurd, even to clever men, that they 
could not help laughing when his papers were read, and did 
not even think them worth printing. You will easily un- 
derstand that after this Franklin was ashamed to speak of 
an experiment he meant to make by which he hoped to 
bring down electricity from the sky. So we find that he 
told no one but his son, whom he took with him upon this 
strange expedition. 

Franklin's idea was that if he could send an iron rod up 
into the clouds to meet the lightning, it would become 
charged with the electricity, which he believed was there, 
and would send it down a thread attached to it, so that he 
might be able to feel it. He took, therefore, two light strips 
of cedar fastened crossways, upon which he stretched a silk 
handkerchief tied by the corners to the end of the cross, and 
to the top of this kite he fixed a sharp-pointed iron wire 
more than a foot long. He then put a tail and a string to 
his kite, and at the end of the string near his hand he tied 
some silk (which is a bad conductor), to prevent the elec- 
tricity from escaping into his body. Between the string 
and the silk he tied a key, in which the electricity might 
be collected. 

When his kite was ready he waited eagerly for a heavy 
thunderstorm, and, as soon as it came, he went out with 
his son to the commons near Philadelphia and let his kite 
fly. It mounted up among the dark clouds, but at first no 
electricity came down, for the string was too dry to conduct 
it. But by and by the heavy rain fell, the kite and string 
both became thoroughly wet, and the fibres of the string 
stood out as threads do when electricity passes along them. 
Directly Franklin saw this he knew that his experiment had 



ch. xxix. FRANKLIN S KITE. 257 

succeeded ; he put his finger to the key and drew out a 
strong bright spark, and before long he had a rapid current 
of electricity passing from the key to his finger. The wise 
men of London might now laugh if they pleased, for the dis- 
covery was made; he had drawn lightning from the sky, and 
proved that it was electricity ! Soon after this he made an 
apparatus in his own house for collecting electricity from the 
clouds, which rang a peal of bells when it was sufficiently 
charged for him to make experiments with it. He also 
invented lightning conductors, or iron rods placed near 
high buildings, to act as constant conductors between the 
clouds and the earth, and so prevent those sudden dis- 
charges called lightning. 

Franklin had now earned a great name ; he was made a 
Fellow of the Royal Society, and many honours were paid 
to him by all the countries of Europe. He made many 
other very valuable experiments, and was besides an active 
citizen and politician. He died in 1790, in his eighty-fifth 
year, after a life of hard labour and toil, for which, however, 
he was well repaid by success. 

Discovery of Animal Electricity by Galvani, and of 
Chemical or Voltaic Electricity by Volta, 1789-1800. 
— Only a few months before Franklin died, a new fact had 
been discovered about electricity, which would have given 
the old man great delight if he could have lived to see the 
results. This discovery was made by Galvani, Professor of 
Anatomy at Bologna, or perhaps we ought to say by Madame 
Galvani, for it was her observation which first led her hus- 
band to study the subject. 

Aloysius Galvani was born at Bologna in 1737, and we 
know little of his early life except that, instead of becom- 
ing a monk as he first intended, he married a professor's 
daughter, and became the Lecturer on Anatomy in the 
University of Bologna. He had in his house an electrical 



258 EIGHTEENTH CENTURY. pt. iil 



machine which he used for experiments, and one day in 
1789, as Madame Galvani was skinning frogs for a soup, 
one of Galvani's assistants was working the machine near 
her. Just as the flow of electricity was going on rapidly, 
this young man happened to touch a nerve of the leg of a 
dead frog with a dissecting knife, and to his great surprise 
the leg began to move and struggle as if it were alive. 
Madame Galvani was so much struck by this that she told 
her husband of it directly he returned, and he repeated the 
experiment many times, and found that whenever the flow 
of electricity from the machine was brought near the nerve 
of the frog's leg it produced convulsions. He next tried 
whether lightning brought down upon the nerves of the leg 
would have the same effect, and the experiment succeeded 
perfectly. 

Meanwhile another accident showed him that the con- 
vulsions could be produced without either lightning or an 
electrical machine. He had prepared the hind legs of 
several frogs and hung them by copper hooks upon an iron 
balcony outside his house. As they hung there the wind 
swayed them to and fro, so that the ends of the legs touched 
the iron of the balcony ; and every time they did so he 
noticed that the legs were convulsed just as they had been 
by the electrical machine and the lightning. But this time 
he could not see that any electricity had come near them 
from outside, so he supposed that there must be an electric 
fluid in the leg itself, which passed round every time the 
two ends of the leg were joined by the metal. These dis- 
coveries of Galvani soon became spoken of far and wide 
under the name of galvatiis7?i y and the supposed fluid was 
called the galvanic fluid. 

Among the celebrated men who were attracted by this 
new discovery was Alessandro Volta, Professor of Natural 



CH. xxix. ANIMAL ELECTRICITY. 259 

Philosophy at the University of Pavia, who was born at 
Como in 1745, an d was at this time a well-known natural- 
ist. Not satisfied with merely reading about Galvani's ex- 
periments, Volta tried them himself, and he began to suspect 
that the electricity was not, as Galvani imagined, in the 
frog's leg, but was produced by the two metals, copper and 
iron, upon which the legs had been hung, and which were 
acted upon by the moisture in the flesh. 

Then began a very famous controversy. Volta insisted 
that the electricity came from the metals, Galvani that it 
came from the animal. In each new experiment which 
Galvani brought forward to prove his point, Volta still 
showed that the electricity could be produced without the 
animal, until at last Galvani succeeded in finding a test 
which he thought must silence Volta for ever. Pie found 
that by laying bare a nerve of the leg of a frog, called the 
' crural nerve,' and bringing the end of it to the outside of 
the muscles of the leg, he could produce the convulsions 
without any metal at all. But Volta was not so easily con- 
vinced ; he still insisted that it was the different fluids and 
tissues being brought together which caused the electricity, 
and that there was not a current running through the 
animal. At this point, just when the truth would probably 
have been worked out, Galvani died (in 1798), leaving 
Volta in possession of the field ; and for twenty-eight years 
no more was heard of animal electricity. We know now 
that both the professors were right. Volta was right in 
saying that the convulsions of the frog's legs on the balcony 
were produced by the contact of the two metals in connec- 
tion with a fluid; while Galvani was right in saying that 
there is an electricity in animals which acts without any 
other help. In 1826 an Italian named Nobili repeated 
Galvani's experiment, and having then an instrument called 
13 



26o 



EIGHTEENTH CENTURY. 



pt. in. 



a galvanometer (see p. 365), by which the passage of the 
faintest electric current can be detected, he proved that 
such a current does exist in the frog, and it has since been 
found to be common to all animals. 

Meanwhile, however, Volta had also made a very re- 
markable discovery, namely, that two different metals when 
joined together in contact with moisture, and separated from 
other substances, produce a current of electricity. This 
may easily be tried in its very simplest form. If you take 
a halfpenny and a half-crown and put one above your 
tongue and one below it, you will feel nothing remarkable 




Fig. 46. 

Volta's Crown of Cups (Fownes). 

z, Zinc, c, Copper. «, a, b, Connecting wires. The arrows show the course of 
the positive currents. 

so long as the two metals are kept separate, but directly 
you let them touch each other at the ends, a tingling sensa- 
tion will pass through your tongue, proving to you that an 
electrical current is passing between the metals. If you 
put the half-crown under your lip, so that the halfpenny 
may remain outside your mouth, you may, perhaps, even 
see a slight flash when the two metals meet. 

Volta found not only that it was necessary to have mois- 
ture between the two metals, but that some acid put in the 
water greatly increased the strength of the electricity. Fig. 
46 shows the first electric battery which he made, and 



THE VOLTAIC PILE. 



261 



which is the one now commonly used for simple experi- 
ments. In this battery each piece of zinc is joined to one 
of copper, and where the two are not united they are in the 
same cup, so that the liquid acts as a link to them. We 
know now what Volta did not know, that a chemical change 
is going on between the zinc and the acid water, which sets 
the action going, but we do not yet know exactly what the 
electricity itself is. The movement in Fig. 46 begins on 
the left-hand side at z. Here the current is set up by the 
action of the acid and water upon 
the zinc, and is passed on to the 
copper, c ; then along the wire a, to 
the next z, and so on till it reaches 
the last cup, when it is carried by 
the wire b back to the first piece of 
zinc, and so the round is completed. 
This battery is called the ' Crown 
of Cups,' but though it is so simple, 
it has not become as famous as the 
second battery made by Volta, which 
is still called the ' Voltaic Pile ' (see 
Fig. 47). In this battery the metals 
are laid one above the other, and 
have small pieces of card or flannel 
between them which are wetted with 
salt and water. The battery ends 
with a plate of zinc at the bottom, and of copper at 
the top, and these are connected by the wire, a a. The 
action passes round this battery just as it did through the 
cups, and if the wire, a a, is cut in the centre and tipped 
with charcoal (which, being a bad conductor, causes the 
electricity to pass with difficulty), a bright spark will glow 
between trie points as long as the battery is at work. Early 




Fig. 47. 

The Voltaic Pile (Fownes). 

z, Zinc, c, Copper, a, a, Rod 
connecting the top layer of 
copper with the bottom layer 
of zinc. 



262 EIGHTEENTH CENTURY. pt. hi. 

in our own century Sir H. Davy succeeded with a battery 
of 3000 cells in producing a bright luminous arch between 
these points when tipped with carbon, and here we have 
the origin of our present electric light. Volta completed 
his Voltaic pile in 1 800, just at the close of the century, and 
even from this slight sketch you may see what grand strides 
had been made in electricty during the past fifty years. 

Franklin had proved the real action of electricity, had 
shown it to be the same as lightning, and had brought it 
down from the sky. Galvani had proved its existence in 
animals, and led the way to Volta's discoveries ; and Volta 
had produced it in enormous quantities by two metals and 
acidulated water, so as to keep up a constant flow, which 
would travel any distance so long as the circuit was not 
broken. Here, you will see, was the first step towards the 
electric telegraph and the electric light, and though it was 
but a commencement, yet when we reap the benefits we 
must always remember the names of Franklin, Galvani, and 
Volta, as the great pioneers in the science of electricity. 



Chief Works constdted. — 'Lardner's Cyclopaedia, Electricity, Magnet- 
ism, and Meteorology;' Encyclopaedias 'Britannica' and 'Metropo- 
litana,' art. ' Electricity ; ' Franklin's ' Experiments and Observations 
on Electricity,' 1749; Priestley, 'On Electricity,' 1785; Thomson's 
'Hist, of Royal Society,' 1812 ; 'Life of Franklin,' by himself, 1833 ; 
Bennett's 'Text-Book of Physiology ;' Fownes's 'Chemistry;' Wilkin- 
son's ' Galvanism.' 



CH. xxx. MUSICAL VIBRATIONS. 263 



CHAPTER XXX. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

Calculation of Musical Vibrations — Sauveur — Bernoulli, Euler, La- 
grange — Nodes and Segments — Chladni — Plates, Bells, and Gongs 
— Sand Figures produced by Vibration. 

Calculation of Musical Vibrations — Sauveur, 1700. 

— After Newton had published his theory of sound, and some 
clearer ideas prevailed about the manner in which sound 
vibrations are conveyed to the ear, many mathematicians 
occupied themselves in working out the laws of those 
regular sound - vibrations which produce musical notes. 
Among the most celebrated of these were Sauveur (1653- 
1716), Daniel Bernoulli (1700-1782), Euler (1707-1783), 
and Lagrange, of whom we shall speak presently in connec- 
tion with astronomy. 

It will be remembered that Pythagoras by stretching a 
string on a sounding-board (p. 12) had obtained musical 
notes, whose intervals depended upon the lengths into 
which the string was divided. Galileo also had pointed 
out (p. 80), that in order to produce a musical note and 
not mere noise, the shocks given to the air must follow 
each other at regular intervals, and that the more rapidly 
the vibrations strike upon our ear, the higher is the note 
we hear; and two men, Noble and Pigot, had made in 
1676 some very interesting experiments on the divisions of 



264 EIGHTEENTH CENTURY. ft. in. 

stretched strings. But, curiously enough, it was a deaf 
man, or one who heard very imperfectly, who made the 
first accurate experiments as to the number of vibrations 
which produce any particular note. 

Joseph Sauveur, the geometer, was born in 1653. He 
was dumb for seven years after his birth, arid his speech 
as well as his hearing remained very imperfect during his 
whole life. Yet this man, who was a splendid mathe- 
matician, found his greatest pleasure in studying the mathe- 
matical theory of sound. Sauveur had remarked that a 
great confusion was created in music because there was no 
fixed note from which every one could agree to start, and 
in order to get this, it was necessary to fix upon some one 
note of a known number of vibrations. But how were the 
vibrations to be counted ? 

Sauveur devised the following method : — Musicians 
knew already that when two organ pipes of different lengths 
are sounded together, then, because the air-wave in the 
shorter one is driven back sooner than in the longer one, 
the puffs of sound will come more rapidly from the shorter 
pipe, just as the footfalls of a man who takes short steps 
will be more frequent than those of a man who strides. 
Now let us suppose two organ pipes, one, a, 8 feet, and the 
other, b, 9 feet long, a being one-ninth shorter than b, 
the puffs from that pipe will be one-ninth quicker, so that 
by the time a has made nine puffs it will have gained 
one whole step upon b, which will only have had time to 
make eight. Now all the time it is gaining, its puffs will 
come somewhere between those of b, but as soon as it has 
gained one whole stride the two pipes will sound simul- 
taneously. This produces what musicians call ' beats/ or 
loud gusts of sound at regular intervals whenever the two 
pipes sound together, and it is clear that if you count how 



ch. xxx. VIBRATION OF STRINGS. 265 

many of these beats there are in a second, knowing that 
between each beat a must have given nine puffs, you have 
only to multiply the number of beats by nine, and that will 
give you the number of vibrations of the note sounded by 
that pipe. 

Sauveur tried the experiment in this way, and found that 
when he sounded the low c in the 8-foot pipe it gave 122 
vibrations in a second. He afterwards went on to apply 
this to stringed instruments, and made many remarkable ex- 
periments. Through his researches and those of Bernoulli, 
Euler, and Lagrange, it was proved that the sound given 
by a string when struck, depends upon four conditions, 
namely, its length, thickness, weight, and its tension, or the 
tightness with which it is stretched. When any one of these 
conditions is altered the string will give a different note, 
but when two strings are exactly alike in these four re- 
spects they will give the same note, because they will both 
make exactly the same number of vibrations to and fro in 
any given time. If one of them is only half as long as the 
other, it will make two vibrations while the longer string is 
making one, and then it will give a note an octave higher; 
all the other notes between these two can also be sounded 
by altering the relative lengths of the two strings. 

It would be too long to work out here the laws respect- 
ing the intervals between different notes and the lengths of 
the strings producing them, but there are some curious and 
beautiful experiments with stretched strings which help us 
to have some idea of musical sound and its laws. If you 
stretch a string upon a sounding-board and then draw a 
violin bow across it, it will give a musical note. If you 
then touch the middle of the string quite lightly with a 
feather you will get the same note an octave higher, because, 
although the whole string is sounding, yet the feather keeps 



266 



EIGHTEENTH CENTURY. 



pt. in. 



the centre almost still, and the two divisions each vibrate 
twice as fast as the whole string did. 

This is very simple ; but now place the feather so as to 
divide off one-third of the string, leaving two-thirds at the 
other end ; it would seem as if you ought to have two 
notes, one for the short string and one for the long one. 
But you will only get one note, and that will be one-fifth 
above the octave you had sounded just before. That is to 
say, you will get the same note as you would have had if the 
string ended at the feather and the other long piece did 
not sound at all. Yet you can easily convince yourself 
that the whole string is vibrating, and what is still more 
curious, that it has divided itself into three short strings, 
each one of which is vibrating as if it were quite separate 




A stretched string damped at one-third of its length, c, and dividing with a natural 
node, or point of rest, between the remaining two-thirds at b (Tyndall). 

To see this, take three small pieces of light paper bent so 
that they will ride upon the string. Then measure off your 
string into three equal parts and touch one of the dividing 
points (c, Fig. 48), with the feather ; place one of the paper 
riders upon the other dividing point b, and the other two, 
one half-way between a and b, the other between b and c. 
If you now draw the bow across the string between c and d. 



CH. XXX. 



VIBRATION OF STRINGS. 



267 



two of the riders will fly off, showing that the long end of 
the string is vibrating, but the one at &, one-third from the 
end of the string, will remain, showing that at this point the 
string is comparatively quiet. The long part of the string 
has, in fact, divided of its own accord into two parts a, b 
and o, c, each of them of the same length as the one you 
made with the feather. Thus you have three short strings 
all vibrating at the same note, and, therefore, all sounding 
the same note. 

But why should the long end of the string divide itself 
into two parts ? 

To answer this, take a long cord, and fastening one end 
of it to the wall, move your hand so as to make it rise up 
into one great wave-crest, a No. i, Fig. 49. When this wave 



No. 1. 



No. 2. 



No. 3. 




3 
Fig. 49. 

Vibrating cords showing how nodes are formed. 
In No. 2 the line a, b, c, /, e, represents the shape of the cord during one half of the 
vibration, and the line a, g, c, d, <?, the shape during the other half of the vibration. 

reaches the wall it will be reflected, and will return to your 
hand, this time not as a crest, but in the shape of a valley 
or trough, o, and, as the rope is moving very rapidly, this 
will give the spindle-shaped appearance shown in the figure. 
Next move your hand more quickly so as to make a 
crest and a trough, a, b, c, fe, No. 2, between your hand 



268 EIGHTEENTH CENTURY. ft. hi. 

and the wall — this is called a whole wave. By the time 
this wave has reached the wall at e> the end of the rope in 
your hand will have begun to form the trough, a, g, c. 
Now notice what happens — the reflected wave from e 
travels back along e, d, c, and meets there the new direct 
wave, a, g, e } coming from your hand. Therefore, at the 
point c, these two movements will meet, and while the 
direct wave a, g, c, will be wanting to pull the string up to 
make its next crest c y d, e, the returning wave e, d, c, will 
be wanting to pull it down to make its next trough, c, g, a ; 
therefore, at this point the string will remain almost at rest, 
forming what is called a node or knot 

Once past this point, each wave can go on its way, and 
the string will gradually assume the form a, g, e, d, e. In 
this way the vibration will continue in two divisions or 
segments with a node or point of comparative rest c, between 
them. It is not at all necessary that there should be only 
one point of rest in the string ; by moving your hand more 
quickly you can make two nodes and three segments as in 
No. 3, and these may be increased almost indefinitely. 

Now it is an action almost exactly the same as this 
which takes place in the stretched string of a musical instru- 
ment when it is made to vibrate. By holding the feather 
against the string at b, Fig. 48, and thus checking at this 
point the swing of the entire string you formed a node, and 
the vibration caused by the scraping of the violin bow instead 
of having its crest in the middle of the string, had it between 
a and b. This caused the trough to come between b and c, 
and the next crest between c and d. Then the reflected 
wave from d had the same effect as in your swinging rope, 
No. 3, Fig. 49, and in consequence the string was divided into 
three segments with two nodes, b and c. When once this 
vibration is set up, you may remove the feather altogether, 



CH. xxx. CHLADNI ON MUSICAL VIBRATIONS. 269 

for the string will continue to vibrate in the same manner 
till it comes to rest. 

All these facts about vibrating strings were worked out 
by Bernoulli, Euler, and Lagrange. Bernoulli also showed 
how the air vibrates in pipes, and why the note they produce 
depends upon the length of the pipe, and the sharpness 
with which the air is forced into it ; but these experiments, 
though very interesting, are too long to enter upon here. 

Chladni on the Musical Vibrations of Solid Bodies. 
— When it was once known that strings give out different 
notes according to their length, weight, thickness, and 
tension, and also that on any one string different notes are 
produced by the formation of nodes or points of rest, the 
foundation was laid for a full understanding of stringed 
instruments. But musical notes can be produced in a much 
simpler way than this. We know that by merely striking a 
glass or a piece of metal we can get a clear and beautiful 
note, and that these notes are different even in the same 
glass when it is held and struck in different places. For the 1 
explanation of these notes we must go to Chladni , a man 
who, on account of'nis wonderful researches, has been called] 
the " Fat her of Modern Acoustics " or the study of sound. 

Ernst Chladni, the son of a professor of Law at Witten- 
berg in Saxony, was born in 1756, and having the misfortune 
to be the only son of an over-anxious father, his childhood 
was dreary in the extreme. He tells us that though he was 
kindly treated and had good teachers, yet he was never 
allowed to go out of the house alone, or to see any boys of 
his own age except at church. His father, indeed, never 
allowed him to go even into the garden unless the day. was 
unusually fine, so that it is wonderful how he kept his health. 
He was not sent to school till he was fourteen years old, 
and then to so strict a master that he was but little better 



270 EIGHTEENTH CENTURY. pt. IIL 

off than at home. At last, when he was nineteen, he went 
to the university at Leipzig, where he had more liberty, but 
even then his great desire to turn his attention to medicine 
was checked, and his father insisted on his studying law. 
This severe discipline seems to have been very unnecessary 
as Ernst was a quiet, studious lad, and though at one time 
he tells us he was almost driven to run away from home, 
the mere thought of grieving his father was " sufficient to 
detain him. He studied physics and natural history in 
secret, and being passionately fond of music, he took lessons 
on the piano while at Leipzig, but for all this he did not 
neglect his legal studies, and took his degree as Doctor of 
Law in 1782. 

Just in this year, when his future career seemed fixed 
without any hope of change, his father died, and the 
moment he was free he gave up the law for ever and 
turned to science. As he had no fortune, this resolution 
cost him a long struggle with poverty, but his stepmother, 
who loved him as her own son, helped him out of her own 
income, and at last he earned enough by his writings and 
his musical instruments to live comfortably. 

Chladni tells us that when his love of music led him to 
study harmony, he found so much in it that no one could 
explain, that he thought he might make some discoveries 
about musical sound. He had noticed that a piece of 
glass or metal gave out different notes when struck, accord- 
ing to the place in which he held it, but the reason for 
this he could not find given in any book. 

About this time a celebrated physician, named Lichten- 
berg r had devised a way of making electrical figures by 
means of resinous powders scattered on glass. This sug- 
gested to Chladni that if musical notes were produced by 
longer or shorter vibrations with nodes or points of rest, 



CH. XXX. 



CHLADNl'S SAND-FIGURES. 



271 



then, if he scattered sand over a piece of glass and struck 
the glass so that it gave out a note, the sand ought to be 
driven from those places which were vibrating, and to 
collect on the nodes where there was little or no movement. 
Accordingly he took a round piece of brass belonging 
to a grinding-machine, and fastening it by its centre in 
a vice, scattered some sand over it, and drew a violin 
bow across the edge. As he had expected, the sand 
moved away from the bow, and from several other points 
at equal distances round the circle, and arranged itself 




Fig. 50. 
Plates of brass made to vibrate by a violin bow. 

in the form of a star with several points ; at the same time 
the metal gave out a very sharp note, showing that the 
vibrations were very rapid. After many other experi- 
ments he proved that when the bow was drawn gently, so 
as to give out the lowest tone of the plate, the sand 
arranged itself in two lines crossing each other at the 
centre (see Fig. 50). This experiment is not difficult to 
try with a plate of metal or glass and a vice ; it will be the 
more sure to succeed if you place your finger on one of 
the nodes, that is |th of the circle away from the bow so 
as to be sure of getting the lowest note. But you may pro- 
duce the same effect still more simply by taking a common 
finger-glass half full of water, and drawing a violin bow 
gently across the edge at a, Fig. 51. You will then find 



272 



EIGHTEENTH CENTURY. 



PT. III. 




that the water will be agitated in the form of four semi- 
circles, a, b, c, d, while from 
the centre to the four points, 
n, n, n, n, it will be still. The 
reason of this is, that when the 
glass is set vibrating, it assumes 
a slightly oval shape first in 
one direction Q, and then in 
the other 0> an d these two move- 
ments produce a figure such as 
., IG ' SI '. , is shown much exaggerated by 

Water vibrating m glass bowl _ m _ ^^ 

which is giving out a musical the fine lines in Fig. 52. The 
place a, across which your bow 
was drawn will move most, and form the centre of a bulge, 
so will the point c opposite to it, making the dotted oval 
#, n, n, c, n, n ; immediately after, 
the other two points b, d, will 
bulge out in their turn, making an 
oval in the opposite direction; and 
so the water will alternately be 
pushed together and spread out 
at all these four places, but at n, 
n, n } n, it will not be disturbed, 
and so the nodes are formed. 
glass when sounding. You can even produce this figure 

by simply wetting your finger and passing it closely round 
the rim of the glass, for whenever the whole glass vibrates so 
as to give its lowest note, it forms two alternating ovals, and 
leaves the four points at rest. The sounds given out by 
bells, gongs, cymbals, glasses, etc., are all produced by 
this change of shape, which causes them to strike the air 
first one way and then the other, and so produce the 
series of condensations and rarefactions (see p. 168) which 




n 

Fig. 52. 
Changes of figure assumed by a 



CH. XXX. 



CKLADNfS SAND-FIGURES. 



273 



reach our ear. The number of sand-rays may be increased 
on round plates by placing the fingers on different points, 
and checking the vibrations, see Fig. 53. When Chladni 
had made many of these, and worked out their relation to 
the particular note sounded, he went on to experiment on 




Fig. 53. 

square plates, and produced the curious figures given in 
Fig. 54, and many others much more complicated. The first 
of these figures he got by fixing the plate by its centre and 







s-r 


> v.^y 


) 




k& 




/?**%■ 





V*--* 


P^S 


?fc5 


K< 


>>2 


m 


'/r^s 


i^^%\ 



Fig. 54. 

drawing the bow across one of the corners ; the second 
by drawing it across the middle of one of the sides ; and 
the more complicated figures below by placing the finger 
and thumb on various points so as to form artificial nodes. 
The lines of sand on these plates are formed on the same 



274 EIGHTEENTH CENTUR Y. PT. ill. 

principle as the quiet lines of water in the glass, but their ex- 
planation is rather complicated. The first two are the most 
simple; in them the squares marked a a are always bending 
upwards when the other squares b b are bending downwards, 
and the lines between these four squares are therefore motion- 
less, and form nodes. In our day Sir Charles Wheatstone 
has analysed all these vibrations, and shown mathematically 
why they assume the forms which Chladni produced. 

Chladni did not only discover the way in which plates 
vibrate : he also worked out most carefully the whole theory 
of musical sound, and left behind him a 'Treatise on 
Acoustics,' which is still of very great value. He also in- 
vented two musical instruments, the euphone and the 
clavicylinder, which are, however, no longer in use. The 
manner of his death was somewhat singular. At an evening 
party held at the house of one of the professors of the 
Breslau University, he was speaking of sudden death as a 
happy thing when happening to a man whose work was 
done. At eleven o'clock he went home, and the next 
morning he was found dead in his chair ; his watch, which 
he must have been in the act of winding, having fallen open 
at his feet. He had died of apoplexy. 

As we shall not be able to return again to the subject of 
sound, it may be well to state here, that great advances have 
been made in it during the nineteenth century, especially by 
Professor Helmholtz, who has worked out the theory of 
musical sounds most completely, and has also explained very 
fully the structure of the ear, and the manner in which the 
vibrations affect it. 



Chief Works consulted. — Sauveur, ' Memoires ; Acad, des Sciences,' 
1701-1707; Fetis, ' Biog. des Musiciens;' Helmholtz, 'Sensations of 
Tone;' Tyndall, 'On Sound;' Chladni, * Die Akustik ; ' Chladni, 
' Endeckungen iiber die Theorie des Klanges ;' Acad, des Sci. 1786. 



CH. xxxi. BRADLEY AND DE LISLE. 275 



CHAPTER XXXI. 

SCIENCE OF THE EIGHTEENTH CENTURY (CONTINUED). 

Bradley — Delisle — Lagrange — Laplace — Sir William Herschel — 
Binary Stars — Star-Clusters and Nebulse — Motion of our Solar 
System through Space — Maskelyne — Schehallion Experiment- 
Summary of the Science of the Eighteenth Century. 

Astronomical Labours of Bradley and Delisle. — And 
now we must take up once more the history of astronomy, 
which we have neglected since Newton died in 1727. 
Since that time many good astronomers had been occupied 
in making different observations, but the only two who 
need be mentioned were Bradley, the Astronomer-Royal 
(born 1692, died 1762), whose accurate observations of 
the stars laid the foundation of all our knowledge of the 
motion of our Solar System in space, and of the proper 
motions of the stars, and Delisle (born 1688, died 1768). 
Bradley explained two difficult astronomical problems ; the 
first of these is called the aberration of the fixed stars, which 
is an apparent movement of each fixed star in a small circle 
in the heavens, but which is really the combined effect of 
the yearly motion of our own earth, and of the time which 
light occupies in coming down from the stars to us. His 
second discovery is that of the nutation, or slight oscillation, 
of the earth's axis. But these observations are difficult to 
understand, but it is necessary to bear in mind that he 
made them, for they are very important in astronomy. 
Delisle will interest you because he proposed a second 



276 EIGHTEENTH CENTURY. pt. HI. 

method of observing the transit of Venus, which is now 
used at stations where Halley's method (see p. 155) cannot 
I be applied. Delisle's method consists in marking the time 
\ of commencement of the transit in one part of the world 
where it begins earliest, and at another station where it begins 
i latest ; instead of measuring, as Halley did, the duration or 
i length of time occupied by the whole transit as seen at each 
'* place. Halley's method requires the stations to be widely 

apart, east and west, and Delisle's, north and south. 
' — These advances are all that need be mentioned during 
the first half of the eighteenth century, but during that time 
there had been born within a few years of each other three 
men, Lagrange, Laplace, and Herschel, who were to light up 
the close of the century with the most brilliant discoveries. 
The two first of these were Frenchmen, the last, though a 
German by birth, may almost be considered English as far as 
science is concerned ; for though he was born at Hanover in 
1738, of German parents, still Sir William Herschel came 
over to England at the age of twenty-one, and all his dis- 
coveries were made here. It was our King George III. 
who gave him the pension which enabled him to devote 
himself to science, and he made England his home and 
country. His son, Sir John Herschel, who, like his father, 
was one of our greatest astronomers, was born in this 
country. 

Lagrange and Laplaoe. — Louis de Lagrange was born 
at Turin in 1736. His father, who had been Treasurer of 
War, lost all his fortune when his son was quite a child, and 
Lagrange often said that it was partly owing to this mischance 
that he became a mathematician. His talent showed itself 
so early that before he was twenty he was appointed 
Professor of Mathematics in the Military College of Turin, 
where nearly all his pupils were older than himself. From 



ch. xxxi. LAGRANGE AND LAPLACE. 277 

there he went to the Academy of Sciences at Berlin, and 
remained twenty years, during which time he worked 
out most of his celebrated problems. In 1787 he settled 
in Paris, where he died in 18 13, at the age of seventy- 
seven. 

Pierre Simon Laplace was the son of a farmer, and was 
born at Beaumont en- Auge, near Honfleur, in 1749. He, 
too, began work very early in life, for in 1769 the famous 
geometer D'Alembert was so struck with his talents that he 
procured for him the chair of Mathematics in the Military 
School of Paris, and from that time, for more than fifty years, 
Laplace devoted himself to the pursuit of science, never 
letting his active life as a politician interfere with his 
scientific studies. He died in 1827. 

The work which was done both by Lagrange and Laplace 
in astronomy was purely mathematical, and dealing as it did 
with some of the most complicated movements of the 
heavenly bodies, it cannot be rightly understood by any but 
mathematicians. But some general idea may be formed of 
the problems they solved, and we will take these in the 
order of time, for they treated so much of the same ques- 
tions, one taking up the subject where the other left it, that 
it is difficult to separate their work. 

Libration of the Moon accounted for by Lagrange, 
1764-1780. — Long before the time of Lagrange it had been 
known from observation that the moon always turns the 
same side of her globe towards our earth as she goes round 
it, so that we never see, and never can see, more than one 
side of her surface, so long as she has the same movement 
as at present. In 1764 the Acade'mie des Sciences offered 
a prize for a complete explanation of this curious fact, and 
Lagrange was thus led to study the question, which he 
solved quite satisfactorily in 1780. 




278 EIGHTEENTH CENTURY. pt. m. 

Many people find it very difficult to understand how the 
moon can be always turning round upon her own axis, as a 
top spins, and yet always keep the same side towards us ; 
therefore, it will be as well to make a simple experiment 
which explains it quite clearly. Take a round ball and stick 
a pin in one side of it, then turn the ball slowly round like a 
teetotum, and notice as it goes round that the pin points 
successively to each of the sides of the room one after the 
other ; then sew a piece of cotton to the side of the ball 
opposite the pin, and fasten the other end down to the 

table (as at E, Fig. 55). If 
you now roll the ball round 
the table, you will observe 
* ' Fig. 55. tnat tne P m points to each 

Diagram showing why one side of the side Of the TOOm in SUCCeS- 

Moon is always turned towards the s j on as j t £[£ before, showing 
Earth. '. • , ■ , 

m, Ball representing the moon, e, Point that it has been turning slowly 

representing the centre of the earth. Qnce Q ^ Qwn ^ wMq 

/, Pin to mark the side of the moon r 

which is never turned towards the going Once TOUfld the point E, 

eart ' and that, for this reason, the 

same side has been facing e all the time. 

This is the case with the moon as she travels round our 
earth, and Lagrange proved mathematically that it must be 
so, as Newton had already suggested, if the moon's equator 
is not circular, but in the form of an ellipsoid, as in that 
case its longer axis would be acted on by the attraction of 
the earth so as to keep it always in the same direction. 
But Lagrange also showed that as the moon moves in an 
ellipse round the earth, and therefore goes at one time a 
little faster, and at another a little slower, while her rotation 
on her own axis does not vary, she does not keep always 
exactly the same face towards us, but we catch little glimpses 
farther round her globe, sometimes on one side and some- 



ch. xxxi. ORBITS OF JUPITER AND SATURN. 279 

times on the other. This balancing movement is called 
the libration of the moon. 

Laplace works out the Long Inequality of Jupiter 
and Saturn, 1774-1783. — The next calculation about the 
planets was made by Laplace, and is more difficult to under- 
stand. You will remember that Newton showed that ever)' 
planet attracts every other planet, and has some effect upon 
its path round the sun. Now it had been found, by com- 
paring old astronomical tables with later ones, that these 
different attractions had altered some of the ellipses in 
which the planets move ; and both Lagrange and a cele- 
brated mathematician named Euler had tried to calculate 
these changes and find out whether the planets would ever 
come back into their old places. Laplace, however, carried 
the calculation farther than either Lagrange or Euler had 
done, and he showed that the whole machinery does work 
round in the course of a long period. Only two planets, 
Jupiter and Saturn, did not seem to follow this general law, 
but behaved in a very eccentric manner ; for it appeared 
that during the seventeenth century Jupiter had been 
moving more quickly every year and Saturn more slowly. 
If this went on, it was clear that Jupiter would draw nearer 
to the sun, and at last fall into it, while Saturn would go 
farther off, and disappear entirely from our system, and 
this would upset the balance of our planets, and might lead 
eventually to our being all drawn into the sun. 

This was a very serious question, and it was a grand step 
when Laplace answered it, and showed that there was 
nothing to fear, for that, odd as their movements appear, 
these two planets really obey the law of gravitation, and 
will return to their old places like the other planets after an 
immensely long period. He showed that their irregularity 
arises from the fact that Jupiter travels two-and-a-half times 



28o EIGHTEENTH CENTURY. pt. hi. 



round the sun while Saturn travels once, and on this account 
Jupiter is always overtaking Saturn, so that the two planets 
are often near together, or in conjunction, as it is called. 
When this happens, they pull each other so strongly that 
they are drawn each out of its proper path. If they always 
met in the same places, and so were pulled in exactly the 
same direction, they would never right themselves again ; 
but as Jupiter does not quite make three rounds while 
Saturn makes one, their points of meeting vary a little each 
time, and this brings them round at last to their old posi- 
tions. Laplace's calculation of this movement is called 
the long inequality of Jupiter and Saturn. 

Laplace also discovered the reason why the moon goes 
on for a long time moving more and more quickly round 
our earth, and then gradually more and more slowly. This 
problem, which is too long to examine here, was the last 
which remained to complete the proof that Newton's theory 
of gravitation would account for all the movements of the 
heavenly bodies. 

Lagrange proves the Stability of the Orbits of the 
Planets, 1776. — And now, in the year 1776, came La- 
grange's great conclusion. He and Laplace had worked hand 
in hand, proving more and more at every step how beauti- 
fully all the heavenly bodies move in order, so that an 
equal balance is preserved between them all. At last 
Lagrange, taking up all the known facts and uniting them 
in one grand mathematical problem, proved that whatever 
might be the changes, and they are almost infinite, caused 
by all the attractions of the different planets on each other, 
yet in the course of long ages every part of the solar 
system remains stable. Each planet has its appointed road 
along which it travels, through many twists and turnings, 
but from which it cannot escape, for the grand force of 



ch. xxxi. SIR WILLIAM HERSCHEL. 281 

gravitation holds them all in one eternal round about their 
sun. 

These are some of the problems solved by Lagrange and 
Laplace. You cannot expect to understand their full signi- 
ficance, nor must you imagine that these few pages contain 
more than a very small fraction of the work which these 
two mathematicians accomplished. Laplace made some 
beautiful calculations explaining the theory of the tides, and 
you will also often hear him mentioned as the author of the 
2 Nebular Hypothesis,' 1 by which he taught that our earth 
and all the planets were in the beginning formed by the 
condensation of gases and fluid matter. All this, which is 
too difficult to enter upon here, is discussed in his famous 
work, the ' Me'canique Celeste,' published in 1799. But 
the main points to be remembered are that Lagrange and 
Laplace proved the regular order of the movements of the 
planets, and explained all those anomalies which had seemed 
to be out of harmony with Newton's theory of gravitation. 

Sir William Herschel constructs his own Tele- 
scopes, and discovers Uranus, 1781. — William Her- 
schel, who was born in 1738, was one of ten children. 
His father, who was an eminent musician, brought him up 
to follow his own profession, and when William came over 
to England with his regiment, he started in life as a teacher 
of music. The first three years in this country were years 
of hard struggle and privation, but at last he was appointed 
organist at Halifax in Yorkshire, and from there he went in 
1766 to Bath, where he soon became known as a talented 
musician, playing in the Octagon Chapel and at concerts 
and parties with immense success, and attracting a large 
number of private pupils. 

1 This hypothesis had, however, been elaborated before the time of 
Laplace by the celebrated philosopher Kant. 



282 EIGHTEENTH CENTURY. ft. hi. 

It was at this time, in the midst of active work which 
kept him fully occupied all the day, that Herschel began 
those nightly observations which have made his name 
famous. His interest was at first excited by seeing the 
stars through a small telescope only two feet in length ; and 
his desire was so great to be able to penetrate farther into 
the starry depths, that he sent to London to order a large 
telescope. When the answer came, however, he found that 
the price of the instrument was quite beyond his means ; 
and so determined was he to carry out his project, that he 
set to work to construct a telescope with his own hands. 
The first one answered so well that he made several others, 
and at last succeeded in completing one forty feet long. 

From that time he spent the greater part of every night 
in observing the stars, and on March 13, 1781, when he 
was examining some near the constellation Gemini, or the 
'Twins,' he caught sight of one star more conspicuous 
than those around it. Struck by its size, he put a stronger 
magnifying power on to his telescope, and found to his 
surprise that this star became larger, while those round 
it remained as small as before. Now the fixed stars are so 
far off that no magnifying power makes any difference in 
their apparent size ; so Herschel began to suspect that this 
must be a body very much nearer to our earth than the 
stars which surrounded it, and he soon found that instead of 
being fixed, it moved onwards steadily. He thought at first 
that he had discovered a comet, but it was not long before 
his wandering star proved to be a new planet, moving round 
the sun outside Saturn. This planet, which had been marked 
by Flamsteed as a star nearly a hundred years before, is about 
half the size of Saturn, and takes more than eighty-four years to 
go once round the sun. It was first called the 'Georgian star,' 
after George III.; then it was called ' Herschel ;' and lastly 



CH. xxxi. THE PLANET URANUS. 283 

it received the name Uranus, which it still retains. It was 
through this discovery that Herschel became known, and 
George III. gave him a pension of 300 guineas a year, and 
a house near Windsor, in order that he might devote him- 
self entirely to astronomy. 

Star-gauging and Discovery of Binary Stars, 1781- 
1802. — One of the first tasks which Herschel undertook was 
to divide the stars into groups, according to their brightness, 
and to gauge the heavens by estimating the number of stars 
of each order of brightness, thus endeavouring to estimate 
the profundity of space. While he was thus gauging, or 
measuring the distance of the stars by the intensity of their 
light, his attention was arrested by some which appear 
single when seen through a small telescope, but which prove 
to be two stars when they are greatly magnified. A few of 
these double stars were known already when Herschel began 
to observe them, but he soon detected no less than 500 
scattered about in different parts of the sky. 

Now it had always been believed that the reason why 
these stars appeared close together was because one was 
almost directly behind the other a long way off, just as two 
posts standing one at some distance behind the other will 
appear to touch if they are nearly on a line with your eye. 
But this explanation did not satisfy Herschel, for he observed 
that many of the double stars, instead of merely passing to and 
fro in a straight line across each other, as they would appear 
to do in consequence of the movement of our earth in its 
orbit, had another peculiar curved motion, as if they were 
both moving round some point half-way between them. 
This movement was so slow that it was twenty-five years 
before he could be sure about it; but at the end of this 
time he was able to- tell the Royal Society that these double 
or binary stars, as they are called, are not one behind the 
14 



284 EIGHTEENTH CENTURY. pt. m. 

other, but are actual pairs of stars moving round and round 
each other, as if they were connected by a rod suspended by 
its centre, and then set revolving ! 

To understand how great a discovery this was, it is 
necessary to bear in mind that Newton had only been able 
to prove that gravitation acts between the sun and the 
planets ; but here was a reason for believing that even in 
the far-off stars, millions of miles away from our system, the 
same force is holding distant suns together, and keeping 
them in their orbits. This great discovery has been still 
more clearly proved by later investigations, and groups of 
two, three, and even more stars are now known, in which 
these bodies revolve round a common centre, held together 
by the force of gravitation. 

Herschel studies Star-clusters and Nebulae, 1786. — 
The next discovery which Herschel made was quite as 
remarkable as that of the binary stars. As long ago as the 
time of Ptolemy (138 a.d.) five curious stars had been 
observed, which he called 'cloudy stars,' because they 
looked as if they were covered by a mist ; and the number 
of these cloudy masses had been increased by different 
astronomers as time went on. When Herschel turned his 
attention to them he discovered so many that, in 1786, 
he published a catalogue of no less than a thousand, and 
added fifteen hundred more a few years later ! Some of 
these bodies, such as the bright spot called the ' beehive/ in 
the constellation Cancer, were simply clusters of stars which 
could be seen distinctly through a telescope. In others the 
separate stars could not be seen even with the strongest 
magnifying power, but the group looked so much more 
distinct through a powerful telescope than through a feeble 
one, that it seemed most likely the stars were there, if only 
they could be distinguished But a third set of cloudy 



ch. xxxi. CLUSTERS AND NEBULA. 285 

bodies did not appear in the least more separated, even with 
the largest telescopes, and these Herschel called nebula or 
clouds, because he believed they were made up of mere 
masses of matter which had not yet formed themselves into 
stars. 

It was at this point that the grand thought forced itself 
upon his mind that in these nebulae we might be looking 
at the actual beginning of new worlds : and that the creation 
of the different bodies of the universe was not begun and 
finished long ages ago, but is even now going on under our 
eyes. The nebulae he believed to be composed of star- 
matter, out of which stars might be slowly forming, so as to 
be first seen scattered like minute points in some of the more 
hazy star-clusters, and then clearly visible, as in the ' bee- 
hive ' in the constellation Cancer. In those days Herschel 
could get very few astronomers to believe in this idea, but 
you will see in the history of the nineteenth century how the 
discoveries of the spectroscope (see p. 339) have proved that 
the light of some of the nebulae comes from incandescent 
gaseous matter ; so that it becomes extremely probable that 
Herschel was right, and that, in far distant space, star- 
mist is forming into stars, and creating new suns to illumin- 
ate the universe. 

The Motion of our Solar System through Space, 
1783. — The third and last theory which we can mention as 
coming from Sir William Herschel is that of the motion of 
our sun through space. In 1783 he showed from a study 
of the astronomical catalogues of past centuries that the stars 
do not stand in exactly the same places with regard to us as 
they did in ages gone by, and that, therefore, either we or 
they must be moving through space. Now, when everything 
around you appears to be moving backwards, it is most 
likely, to say the least, that it is you who are moving forwards, 



286 EIGHTEENTH. CENTURY. ft. in. 

and not that all other things are in motion ; therefore Her 
schel concluded that the reason of the apparent change in 
the place of the stars was the real movement of our sun and 
its planets among them. 

But, if such were the case, then there ought to be one 
point straight in front of our path which would not appear 
to move ; for if you walk into a forest, you will observe that 
the trees on either side appear to spread farther and farther 
apart as you approach, but that those exactly in front of you 
will not seem to change their places. Now Sir W. Herschel 
found one point in the sky, in the constellation Hercules, 
where the greater number of the stars do not appear to move, 
while those to the right and the left seem to be gliding off 
each in their own direction. He therefore concluded that 
our sun is carrying the earth and the other planets straight 
towards this point in the constellation Hercules. The rate 
at which this movement goes on is not accurately known, 
but it must be very great, probably at least as much as 
150,000,000 miles every year. 

And here we must leave the discoveries of this great 
astronomer, although we have only glanced at them very 
superficially. The immense strides in astronomy made by 
Laplace, Lagrange, and Herschel cannot be understood in a 
moment ; and I wish you always to remember that you can 
only gather crumbs of knowledge from this book, which 
may, I hope, lead you to long and seek for more solid food. 
Before, however, we take leave of Sir W. Herschel, we 
must not forget to mention the faithful assistant who was so 
great a help to him in his labours. 

When George III. gave Herschel his home and pension, 
the astronomer sent to Hanover for his sister Caroline, and 
she lived with him and received a small salary as his assist- 
ant She shared his night-watches and mapped down the 



CH. xxxr. THE DENSITY OF THE EARTH 287 

stars, star-clusters, and nebulae, as he came across them 
with his slowly-moving telescope ; she helped to draw up 
his catalogues, to write his papers, and to make his calcula- 
tions. In a word, she fulfilled one of the highest duties of 
a woman, in becoming the patient helpmate of a great and 
noble mind ; and for this reason, although she never sought 
fame for herself, the name of Caroline Herschel will always 
be associated with the labours of our great astronomer. Sir 
William died in 1822, in his eighty-fourth year, leaving 
behind him a son, the late Sir John Herschel, who will be 
mentioned in the next chapter. 

Determination of the Density of the Earth by the 
Schehallion Experiment, 1774. — After speaking of the 
wonders of the vast universe, and of suns so distant that we 
cannot even guess at the space which lies between them 
and us, we must now come back to our little planet and 
mention a remarkable experiment which was made in 1774 
by Maskelyne, who was then Astronomer-Royal of England. 
This was the finding out of the weight of the earth com- 
pared to its size, or, in other words, the density of the earth. 

If our globe were made of one material, it would be easy 
to weigh a small piece and multiply that by the size, which 
we know pretty accurately, and so to get at the weight of 
the whole. But as the rocks of the earth's crust differ very 
much in weight, and we do not know what the middle of 
the globe is made of, this plan is not possible. We know, 
however, that every atom of matter has the power of attrac- 
tion, so that if we could find out how much attraction our 
earth possesses, by comparing it with the attraction of some 
other body which we can weigh, then we could arrive at the 
weight of the earth. 

Now Newton, in his ' Principia,' had pointed out that a 
plumb-line, that is, a piece of string with a weight of lead at 



2 S8 



EIGHTEENTH CENTURY. 



VT. III. 



the end of it, will not point straight to the centre of the 
earth when it is held near a mountain, because the moun- 
tain attracts the lead and draws it slightly towards itself. 
Therefore, if the size and weight of the mountain were 
known, and it were also known how great its pull is com- 
pared to the pull of the whole earth, this would enable a 

mathematician to calculate 
the weight of our entire globe. 
A man named Bouguer 
was the first to make this ex- 
periment near a high moun- 
tain in Peru in 1738, but he 
succeeded very imperfectly, 
and in 1772 Maskelyne pro- 
posed to the Royal Society 
to repeat the observation. 

Accordingly, he went in 
1 7 7 4, to a very high mountain 
called Schehallion, near Loch 
Schehaiiion Experiment for estimating Tay, in Perthshire, and there 

the Density of the Earth (Herschel). he measured the inclination 
A b, Surface of the earth. D, c, D, Angle , r , , , , ,. 

formed by the two plumb-lines point- °* slope of the plumb-lme On 

ing to the centre of the earth, e, g, eacn S [^ Q f tns mountain. 
E, Angle formed by the two plumb- 

lines when drawn aside by the moun- YOU Will remember that, aC- 

tainMl cording to the theory of 

gravitation, the lead at the end of the line would 
point straight to the centre of the earth c if the mountain 
did not disturb it; 1 and if the plumb-line is taken to two 
places a certain distance apart and its inclination- measured 
by means of one of the stars overhead, it is easy to find out 

1 This is not strictly true, on account of bulge at the equator and 
flattening of the poles ; but the discrepancy is of no importance to the 

argument. 




ch. xxxi. THE SCHEHALL10N EXPERIMENT. 289 

exactly how much the lines d f will slope towards each 
other when no mountain is between them. This measure- 
ment being known, Maskelyne then made two observations, 
one on each side of Schehallion, and found that in this case 
the inclination, instead of being from d to F on each side, 
was from e to f, because the mountain drew the lead to- 
wards itself on either side. So the deflection efd, through 
which the plumb-line was drawn from the perpendicular, 
showed the difference between the pull of the whole earth 
and the pull of the mountain. 

Then Dr. Hutton, the celebrated geologist, set to work 
to find out the size and weight of Schehallion. This he did 
by surveying it and measuring it in every direction, and 
then taking pieces of the different rocks it contained and 
weighing them carefully. When this was done, it was found 
that the mountain pulled half as strongly in comparison to 
its size as the earth did for its size. This showed that the 
materials in the mountain were half as heavy as the average 
of those in the earth generally, and as they were also about 
z\ times as heavy, bulk for bulk, as water, it was proved that 
the whole globe is about five times heavier than it would be 
if it was made entirely of that fluid. 

This calculation must be very near the truth, for the 
chemist Cavendish obtained nearly the same result from 
quite a different experiment made with suspended balls. 
This, which is called the 'Cavendish experiment,' is too 
difficult to explain here. In our own times, Francis Baily, 
Sir Henry James, Sir Edward Sabine, and others, have re- 
peated these observations, and found them to be correct. 

Summary of the Science of the Eighteenth Century. 
— This sketch of the advance of astronomy brings us to the 
end of the science of the eighteenth century ; for although 
the greater number of the eminent scientific men of our day 



290 EIGHTEENTH CENTURY. PT. ill. 




were born before the year 1800, yet their works belong 
chiefly to the nineteenth century. Before going farther, 
therefore, we must now look back and see how far science 
has travelled since our summary of the seventeenth 
century. 

Biology, or the science of life, had made great progress. 
It had been enriched by the study of organic chemistry, 
founded by Boerhaave, by which we learn the elements of 
which living bodies are composed ; by a more complete 
knowledge of anatomy, or the structure of the body in all 
its most minute parts, as Haller studied and represented 
them in his anatomical works ; and by a knowledge of 
comparative anatomy, as taught by John Hunter, or the 
comparison of each organ as it appears in different beings, 
from the lowest animal up to man. But even now the chief 
point remains to be mentioned, for all these^are of little use 
without the study of physiology, or the science of living 
beings, in which we must not only learn the great facts of 
the working of our own bodies and those of animals, but 
must take into account the strange freaks of nature taught 
us by the experiments of Bonnet and Spallanzani. In the 
history of the nineteenth century we shall have to consider 
some of these facts, and see how Cuvier, Lamarck, and 
Darwin have carried out the study of physiology to great 
results in our own day. But we have still more to include 
under Biology. After learning the nature of living beings, 
we must have some order of arrangement by which we can 
distinguish them. Here we come to the work of Linnaeus, 
one of the grandest men of the eighteenth century. While 
Buffon was popularising natural history, we find the great 
Swede patiently working out all the minute characters and 
general features of animals and plants, and reducing the 
whole kingdom of life into such beautiful order, that after 



OH. xxxi. SUMMARY. 291 

his time it could be studied accurately and usefully by all 
who cared to take time and trouble. 

Thus, even without mentioning the science of medicine, 
which had grown far beyond our power of following it up ; or 
the wonderful work with the microscope, which had increased 
rapidly since the days of Grew and Malpighi, biology grew 
during the eighteenth century into a group of sciences, the 
works upon which would fill a library, and each branch of 
which requires the study of a lifetime to master it. 

Geology — Side by side with biology arose, about this 
time, the modest and almost unnoticed science of the earth, 
then generally called physical geography, but now known as 
Geology. This was a small seed sown in the eighteenth 
century, to grow into a large tree only in our time ; yet it 
was a great step when Scilla insisted that fossils were the "" 
remains of living beings, and that the rocks containing them 
were formed gradually under lakes or seas. And when 
Werner taught men to study the earth's crust, and Hutton 
forced them to see that Nature is, and has always been, 
building up our present world out of the ruins of the past, 
the foundations were laid for the real study of the earth and 
its formation. Meanwhile William Smith toiled over 
England, mapping out the position of each rock as he saw 
it, and thus he led the way to a long series of careful 
observations, by which the whole geology of England has 
been worked out. 

Chemistry. — But the science which before all stands 
forth in the eighteenth century is chemistry ; for here the / 
discovery of the different gases led to certainty where all had 
been guess-work before, showing the actual chemical changes 
which are taking place on all sides in the world around us, 
and teaching men to weigh and test invisible substances, and 
not to rest satisfied with their knowledge of any substance 



292 EIGHTEENTH CENTURY. ft. hi. 

till they have traced it home to its first and simplest elements. 
We need not recapitulate here the different discoveries of 
Scheele, Bergmann, Black, Cavendish, Priestley, and La- 
voisier. You will remember how they all helped to overthrow 
the theory of Phlogiston, and to prove that combustion and 
respiration are merely chemical changes taking place between 
different substances and the oxygen of our atmosphere \ and 
this truth is the starting-point of modern chemistry. 

Physics. — In physics the three subjects in which we 
have noticed advances are those of sound, heat, and elec- 
tricity. In the first of these the interest is chiefly theoreti 
cal, and we learn how the melodies and harmonies which 
are so pleasing to our ears are the result of vibrations act- 
ing under fixed laws, so that we can calculate with the 
greatest exactness what are the movements of any particular 
body giving out a musical sound, and can even convert the 
sound, as it were, into a visible figure in which we can read 
the history of the note's production. The discoveries in the 
other two subjects, heat and electricity, are of great practical 
interest, and have caused greater changes throughout the 
world than any previous discoveries. When Black proved 
the amount of heat which is lying hid in water and in 
steam, and when Watt applied it to the steam-engine, a 
giant power was born into the world which has worked 
marvels. Visit any of the little towns all over England and 
see the machines of all kinds moved by the simple power of 
steam ; then go to the great manufacturing towns and see 
the huge engines doing the work of thousands of horses, 
with no other help than that of a man feeding the furnace 
with coals. Look at any one of your own clothes, at the iron- 
work in all parts of your house, from the rough heavy iron 
of fireplaces and fenders to the delicate steel spring which 
moves the hands of your watch ; look at the planks on yoiu 



ch. xxxi. SUMMARY. 293 

floors, and the carpets which cover them ! All these have 
been woven, and forged, tempered, sawn, and worked by 
steam machinery. Then think of the way in which people 
are carried from one place to another of the world ; so that 
in one month a man may be in India, and the next in 
London ; while food, clothing, and goods of all kinds are 
spread over different countries in a few weeks wherever they 
are most wanted. And then remember that all this has 
sprung out of the latent heat of steam, and its application 
by Watt to the steam-engine. 

The next discovery is perhaps even more wonderful. / 
Franklin tries ^experiments upon the peculiar power known I 
by the name of electricity ', and he suspects that it is every-! 
where and in everything. He proves its transmission from 
one body to another, and finds out many of its properties. 
In spite of the derision of his friends, he seeks to bring it 
down from the sky, and succeeds in making a prisoner of 
the lightning and working with it in his own laboratory. 
Galvani next finds this wonderful power hidden in the nerves 
of a frog ; while Volta crowns the whole by showing that 
electricity can be produced by two metals placed in a little 
acid and water, and that this can be carried along a wire of 
any length which touches the battery at both its ends. 
Here lies hid the germ of the electric telegraph ; but the 
grand secret of carrying messages from one end of the 
world to another in a few moments was not to come yet. 
That remained for the nineteenth century to accomplish. 

Astronomy. — Lastly we come to astronomy, and to 
some of the most tremendous problems in the working of 
our universe. Here we find Lagrange proving that the 
system of our sun and planets is self-regulating, so that in 
spite of all its infinite changes there is no real irregularity 
or changeableness in its machinery, but all moves in one 



294 EIGHTEENTH CENTURY. PT. m. 

perfect and constant round. Laplace shows the reason of 
those irregularities which seemed to contradict Newton's 
law of gravitation, and proves that they are all explained by 
that law, thus completing the work of the great astronomer. 
Then Herschel takes up the story, and after discovering a 
new planet, he studies the cloudy nebulae, and points out 
the probable formation of new suns going on now in far- 
distant regions ; he pictures our own sun rushing through 
space at the rate of 150,000,000 miles a year, carrying with 
it our earth and all the other planets ; and above all he traces 
the law of gravitation into the distant star-world, and shows 
it there holding suns together and causing them to revolve 
round each other. And so, out into space as far as the 
mind can reach, we find everlasting order reigning through- 
out the visible universe. 



List of Works consulted. — Herschel's 'Astronomy;' Arago, 'Vie 
et travaux de Herschel,' 1843; Proctor's 'Essays on Astronomy,' 
'The Universe,' 'Other Worlds than ours;' Grant's 'History of 
Physical Astronomy;' Arago, ' Eloge of Laplace;' Airy's 'Astro- 
nomy ;' * Encyclopaedia Britannica ' — ' Astronomy j' ' Orbs of Heaven,' 
Mitchell. 



SCIENCE OF THE 
NINETEENTH CENTURY 



In this List are mentioned only the chief of those Men 
of Science of the Nineteenth Century whose dis- 
coveries are treated of in the following pages. 

Those whose death is left blank were living in 1883. 



Piazzi • • 


AD. 

1746-1826 


•Wollaston . 


A.D. 

, I766-I828 


Ol hers . 


1758-1840 


Biot 


1774-1862 


Encke « . 


1791-1865 


Berzelius • 


1779-1848 


Gauss . 


1777-1855 


Dalton . . 


. I767-1844 


Sir J. Herschel 


1792-1871 


1 'Davy . . 


. I778-I829 


Airy . . . 


1801 


Faraday . 


I79I-I867 


Adams . • ■ 


1818 


Liebig . 


I803-1873 


Leverrier . . 


1811-1877 


? Graham . 


I805-I869 


Galle . 


1812 


Andrews . 


. I8I3 


Schwabe . , 


1788-1875 


Avogadro • 


. 1731-1813 


Watson . . i 


1838-1880 


Wohler 


, I800-I882 


Asaph Hall . 


1829 






Young . . 1 


1773-1829 


Humboldt 1 1 


1767-1835 


Malus . . t 


1775-1812 


Buckland • 


I784-I856 


Fresnel . . • 


1788-1827 


Lyell 


1797-1875 


Arago » . . 


1786-1853 


Murchison . 


1792-1871 


Seebeck - > 


, 1770-1831 


Sedgwick . 


1737-1873 


Oersted j , 


1777-1S51 


Agassiz . 


I807-I873 


Ampere • 


. 1779-1864 


Boucher de Perthes 


1788-1868 


* Brewster . 


, 1784-1868 


Hooker, Sir W 


. I785-I865 


Sabine . . 


. 1788-1883 


Sprengel 


, I750-l8l6 


- Fraunhofer . 


. 1787-1826 


A. de Jussieu 


. I748-I836 


Herapath . 


. 1796-1868 


R. Brown . 


• 1773-1858 


* Clausius . 


, 1822-1888 


De Candolle . 


I778-I84I 


Wheatstone . 


. 1802-1875 


Lindley . 


, I799-I865 


* Bunsen . 


. 1811 


Endlicher . 


, I 804- I 849 


Fizeau . . 


, 1S19 


Von Mohl . 


, I805-I872 


Foucault e 


. 1819-1868 






* Rumford . 


. 1753-1814 






Mayer . . 


. 1814-1878 


Lamarck . 


. I 744- I 829 


• Joule . 


. 1818 


Goethe . 


1749-1833 


• Thomson, Sir W. 


. 1824 


Cuvier . 


I769-1832 


Helmholtz 


. !8 2 J[ 


G. St. Hilaire 


. I772-I844 


Weber . 


, 1804 


Von Baer . 


, I792-I876 


Clerk-Maxwell 


. 183I-1879 


Wallace . 


, 1822 


♦Kirchhoff 


. 1824 


Darwin . 


I809-I882 


Tyndall # 


, J820 


Herbert Spencer 


I820 


. Huggins 


, 1824 


Huxley 


I825 


Miller . 


, 1817-187O 


Owen . . 


I804 


• Crookes 


, I832 


Balfour . , 


I85I-I882 



ch. xxxn. ASTRONOMY. 297 



CHAPTER XXXII. 

SCIENCE OF THE NINETEENTH CENTURY. 

Difficulties of Contemporary History — Olbers — Asteroids — Enche's 
Comet — Biela's Comet — Adams — Leverrier — Discovery of Neptune 
— Sir John Herschel — Comets and Meteor -systems — Improved 
Telescopes — Leverrier's analysis of Planetary Orbits. 

We have now arrived fairly at the beginning of our own 
century, and shall have to speak of events which happened 
as it were but yesterday, and of men whom our grandfathers, 
or even perhaps our fathers, have seen and known. How 
are we to find our way through the mass of discoveries 
which have been made in every science during the last 
seventy years, or to make our choice among the number of 
famous men whose names we meet with every day? We 
must begin at once by recognising that it is impossible to 
mention all, even of the leading points, of the science of 
our time, and then we may try to learn a few of them, if we 
do so with a clear understanding that we are leaving im- 
portant gaps unfilled. 

There are two special difficulties which we must en- 
counter in the history of this century; first, we cannot 
avoid mentioning the work of some living men, while at the 
same time we omit others who are equally eminent ; and 
secondly, we must speak of many subjects which are still, as 
it were, on their trial, and which will not be finally settled 
till they can be judged dispassionately by future generations. 



298 NINETEENTH CENTURY. pt. hi. 

I have tried, however, to follow as far as possible the plan I 
adopted in the earlier centuries, of mentioning only a few 
great men whose work you can understand and follow ; and 
stating on doubtful subjects what is the opinion of those who 
are best able to judge from the evidence. Therefore you 
must constantly bear in mind that this last portion of the 
book cannot be said to contain a history of the science of 
the nineteenth century, but only an account of a few of the 
leading discoveries and theories of our times and of the 
men who made them. 

Advance in Astronomy. — The science of Astronomy, 
in particular, has spread far beyond our power to follow it. 
We have seen that astronomers, up to the end of the 
eighteenth century, were always striving to work out the laws 
which govern the movements of the heavenly bodies. The 
key to this problem was found by Newton, and the work was 
so far completed by Laplace and Lagrange as to show that 
even those planets which seem to have the most irregular 
orbits are really governed by the force of gravitation. From 
that time astronomy became an exact science, and men had 
only to make their calculations with perfect accuracy in 
order to be able to foretell what was going to happen ; or, if 
they failed, then they knew there must be some other un- 
known heavenly body (such as Neptune, p. 302) causing the 
irregularity. Therefore the science of astronomy in our 
century has been chiefly occupied in recording, with ever 
increasing accuracy, the positions of the heavenly bodies — 
sun, moon, planets, and stars ; and it is from the discussion 
of these observations that Leverrier has been enabled to 
produce his theories of the planets, and that Hansen, 
Pontecoulant, Delaunay,. and Adams have perfected the 
theory of the complicated motion of the moon. And side 
by side with this has grown up a new study, namely, that 



ch. xxxii. ASTEROIDS OR MINOR PLANETS. 299 

of the nature of the sun, planets, stars, comets, meteors, 
etc., telling us what they are like in themselves, whether they J 
have an atmosphere like our own, and of what materials ' 
they are made. This study has been carried on partly by 
powerful telescopes, but chiefly by the wonderful method 
called spectrum analysis, of which we shall speak presently. 
Meanwhile we must first begin by naming a few new bodies 
lately observed in the heavens. 

Discovery of the Asteroids and Minor Planets be- 
tween Mars and Jupiter, 1801-1807. — Not long after the 
discovery of Uranus, a well-known astronomer named Bode 
pointed out that the distances of the planets from the sun 
seemed to follow a remarkable arithmetical law. The only 
exception to this law was between Jupiter and Mars ; and 
here the gap was twice as large as it ought to be according 
to the calculation. Therefore astronomers suspected (as 
indeed Kepler had suggested more than 200 years before) 
that there must be a planet between these two which had 
not yet been seen; and in the year 1800, at a meeting 
at Lilienthal, in Saxony, they agreed to search diligently for 
this supposed missing body. 

Signor Piazzi, the Astronomer of the Observatory at 
Palermo, in Sicily, was one of these planet-seekers, and on 
the first night of the year 1801 he caught sight of a small 
star in the constellation Taurus, which had not yet been 
noticed in any catalogue. The next night he looked for it 
again, and found that it had moved its position. He did 
this for twelve nights, and the movement seemed to show 
that it must be the planet he was seeking. Just at this point, 
however, he was taken ill, and although he had told other 
astronomers of what he had seen, no one could find the 
planet again. Months passed, and people began to doubt 
whether he had not made a mistake ; but at last a young 



300 NINETEENTH CENTURY. PT. in 

German astronomer, named Gauss, set to work to calculate, 
from the facts which Piazzi had given, whereabouts in the 
heavens the planet ought then to be, and turning his tele- 
scope to the point, there he found it ! This planet was 
called Ceres ; it was very small compared to the other 
planets, but the astronomers were satisfied at having filled 
up the supposed gap. 

Before two years had passed away, however, in the year 
1802, Dr. Olbers of Bremen announced that he had found 
another little planet near Ceres, which he called Pallas, and 
in 1804 a third was found by another astronomer named 
Harding, who called it Juno. It seemed very strange that 
so many bodies should be moving round the sun at nearly 
the same distance from it, and Dr. Olbers suggested that 
they might perhaps be parts of one large planet which had 
broken up into fragments. If this was so, he expected to 
find more, and truly enough, in 1807 a fourth was dis- 
covered, which he called Vesta. In 1845 and 1847 two 
more were added to the number. Since then some have 
been found every year; in May 1883 the number of these 
small planets, or asteroids as they are called, moving round 
the sun between Mars and Jupiter, had reached to 232, and 
new ones are always being discovered Ceres, the largest 
of these, only measures about 196 miles across, and when 
it comes nearest to the earth does not look larger than a 
star of the eighth magnitude. Whether they are really 
fragments of a planet is not proved, and we have still a great 
deal to learn about them. 

Encke's Comet, 1819. — The next bodies of interest 
which were discovered were two returning comets, each of 
them remarkable for different reasons. The first of these 
was observed in 1819, through the telescope at Marseilles, 
by a Frenchman named Pons. It was very small, and is 



CH. xxxii. RETURNING COMETS. 301 

mainly of importance because, after Professor Encke of 
Berlin had calculated that it returned regularly every three 
years and a quarter, he found that it arrived two hours and 
a quarter earlier each time. Why it should come earlier is 
a question which is still very perplexing to astronomers, 
though several explanations have been suggested. In order 
to find out how fast this comet moved, Encke was obliged 
to calculate very accurately how much the different planets 
attract it ; and this led him to discover that the mass of 
Jupiter is greater than the earlier astronomers had supposed, 
while that of Mercury is much less. 

Biela's Comet, 1826. — In 1826 another remarkable 
comet was observed by an Austrian officer named Biela, 
and on that account called ' Biela's comet.' M. Clausen, a 
German astronomer, computed that it revolved in an elliptic 
orbit in a period of six years and eight months, and it was 
then shown to be-the same comet which had been observed 
in 1772, 1805, and 18 18. This comet has had a very 
curious history. In the year 1832 great alarm was excited 
because the astronomers had calculated that it would cross 
the orbit of our earth on October 2 9. People who did not 
understand the question thought this meant that it would 
run into us and perhaps destroy our earth ; and many even 
sold their houses and land because they thought the end of 
the world was at hand. The people in Paris especially 
were so frightened about it that the Academy of Sciences 
thought it advisable to ask Arago, the French astronomer, 
to quiet their fears, and he wrote a popular essay, showing 
that though the comet crossed the path of our earth, yet on 
that day we should be fifty-five millions of miles away from 
the spot. 

But it was in 1845 that Biela's comet proved most in- 
teresting. On November 26 in that year it came at the 



302 NINETEENTH CENTURY. pt. in. 

time it was expected, and was seen each night afterwards as 
usual till January 12. On that night, however, when 
Lieutenant Maury looked at it from the observatory at 
Washington, in the United States, he saw, not one comet, 
but two distinct and separate comets moving along together. 
This seemed so strange that it would scarcely have been 
believed if several astronomers had not watched the comet 
for more than a month, and satisfied themselves that it had 
really split up into two parts, each part being a perfect 
comet, with a bright head and a glowing tail ! These two 
comets returned in 1852, still keeping each other company 
at the same distance apart as in 1846, but since then they 
have never been seen again. Many other comets have been 
discovered besides these, and it is probable that many thou- 
sands or even millions must be wandering through space, 
but of these we cannot speak here. 

Adams and Leverrier determine the Position of 
an Unknown Planet by its Influence on the Orbit of 
Uranus, 1843-1846. — The next discovery which we must 
consider is one of the most remarkable in the history of 
astronomy, because it was not made with the telescope, but 
was worked out independently by two men entirely by 
means of Newton's theory of gravitation. You will remem- 
ber that in 1 7 8 1 Sir William Herschel discovered the planet 
Uranus moving outside all the other planets (see p. 282). 
Now, many astronomers had noticed this body in earlier 
ages, and supposing it to be a star, had marked its position 
from time to time in the heavens, and from these observa- 
tions it was now possible to calculate its path round the sun. 
When this was done it was found, however, that the planet 
did not move as it ought to do according to the theory of 
gravitation. The pull of the sun and the known planets 
did not account for its orbit, for it roamed farther out into 



ch. xxxii. DISCOVERY OF NEPTUNE. 303 

space than it should do if they were the only bodies which 
attracted it. Either, therefore, the early astronomers had 
marked the position of the planet wrongly, or some un- 
known and unseen body must be pulling it out of its course. 
This last seemed the most likely explanation, but no 
such planet could be seen, and the problem remained 
unsolved. 

It was at this point that a young student of St. John's 
College, Cambridge, named John Couch Adams, then only 
twenty-three years of age, made a memorandum in his note- 
book to work out the movements of Uranus, and see if by 
this means he could discover whether there was another 
planet farther away from the sun. As soon as he had taken 
his degree as Senior Wrangler in 1843, he set to work to 
carry out his intention, and two years afterwards, in October 
1845, he sent a paper to Mr. Airy, the Astronomer-Royal 
at Greenwich, stating in what part of the heavens astro- 
nomers ought to look for the unknown planet which would 
explain the' capricious movements of Uranus. 

It is not easy for any but mathematicians to understand 
what a wonderful thing it was to calculate accurately, in this 
way, where a planet would be found which had never been 
seen. When Pallas was discovered between Mars and Jupi- 
ter, Piazzi saw it through the telescope for some days, and 
it was only found again by following out the movement 
which he had recorded. But in Adams's case nothing had 
ever been seen, and the only reason for suspecting anything 
to be there, was that astronomers could not make their very 
difficult calculations of the attraction of the different planets 
come out right. Adams, therefore, had first to calculate all 
the attractions of the sun and the planets, in their different 
positions, and then to find out how they would affect Uranus 
in his path \ and wherever the planet did not follow their 



3°4 NINETEENTH CENTURY. ft. ill. 

pulling he had to calculate where another body must be to 
draw it away from them. This he accomplished, and it is 
very remarkable that the great French astronomer Leverrier 
also worked out the same problem, without having heard 
that Adams had done it. 

In the year 1838 Leverrier had begun a long series of 
calculations, which were only completed in 1874 (see p. 461), 
to find out the varying attractions, and by that means the 
size and weight, of the different planets, and while he was 
at work at this he became convinced that there must be some 
unseen body pulling at Uranus. Now it so happened that 
just at the time when Adams and Leverrier began to feel 
after this supposed planet, Uranus had lately been very 
much disturbed, and so they knew that he must have 
approached near to the disturbing cause, and this showed 
them in which part of the heavens the attracting planet 
ought to be. 

Leverrier published his calculations in the Journal of 
the Academie des Sciences at Paris in November 1845 and 
June 1846, and when the Astronomer-Royal read the papers 
he was astonished to find that the French astronomer had 
fixed the place of the unknown planet within one degree of 
the spot which Adams had named. This led him to suggest 
that a search should be made for it, and Professor Challis 
of Cambridge actually observed and recorded its place on 
August 4 and 12, 1846, but having no chart of that part 
of the heavens, was not able to identify it. Meanwhile 
Leverrier published another paper on August 31,1 846, stating 
still more accurately where the planet ought to be found. 
This paper he sent to his friend M. Galle, of the Berlin 
Observatory, on September 23, 1846, asking him to look in 
that part of the sky which he pointed out. M. Galle did so, 
and 011 that same nighty by following out the instructions, found 



CH. xxxil. SIR JOHN HERSCHEL. 305 



the unknown planet, which he identified from a chart in his 
possession. So true is the law of gravitation, that two men 
sitting at home in their studies were enabled, from slight 
irregularities in the motion of Uranus, to predict the ex- 
istence and place of a disturbing body, rolling on through 
space ! This new planet is called Neptune. It is a little 
larger than Uranus, but so far off that it is not visible to 
the naked eye. It has certainly one moon, discovered by 
Mr. Lassell. 

Sir John Herschel's work in Astronomy. — While 
these different discoveries were being made in the obser- 
vatories of Europe, Sir John Herschel was at the Cape, 
sweeping the heavens with his telescope for double stars and 
nebulae, and measuring their brilliancy. Born at Slough, 
close to his father's observatory, in 1792, the young John 
Herschel spent his early life with his father and aunt, 
and saw them always busy night and day studying the 
heavens. In 18 13 he was Senior Wrangler at Cambridge, 
and after that he turned his attention to double stars, 
and in 1818 completed a list of no less than 2000 of 
these wonderful double and sometimes treble suns which 
revolve round each other. When he had completed the 
survey of the whole of our northern skies, he went in 1833 
to the Cape of Good Hope, taking with him a large tele- 
scope, for which he built an observatory, and there he 
spent four years gauging the stars of the southern hemi- 
sphere, and classing them according to their brilliancy, as 
his father had classed those of the northern hemisphere. 
He was thus the first astronomer who swept his telescope 
over the whole of the heavens which are visible from our 
planet, and who saw with his own eyes every star, planet, 
and nebula, then visible in the sky. Among the remark- 
able appearances which he examined were those cloudy 



306 NINETEENTH CENTURY. pt. in. 

masses of light called the Magellanic Clouds, which are a 
portion of the Milky Way of the southern hemisphere, and 
he found them to be made up of stars, star-clusters, and 
nebulae, mingled together in wonderful complexity. 

When he returned to England in 1838, you can imagine 
what a wonderful picture he must have had in his mind of 
the whole universe, as far as we can see it. It was then that 
he wrote his famous ' Outlines of Astronomy,' which was a 
new edition of a little book he had written years before. In 
this great work Sir John Herschel first taught ordinary 
people what a grand science astronomy is. Before his time 
the different discoveries and theories had been scattered 
about in various scientific papers, too difficult and too 
tedious for the public to read. But Sir John wrote simply 
and plainly about the great truths which had been worked 
out, from the days when Aristarchus first asserted that the 
earth moved round the sun, to the time when Sir William 
Herschel pictured our whole solar system travelling onwards 
through endless space; and through his book many who 
would never otherwise have studied the science learnt to 
know something of the wonders of the heavens and the 
lessons they teach. Sir John was a true lover of the works 
of nature, and he taught all his readers to love them too, 
and to feel a true reverence for the Infinite Mind of the 
Creator of them alL He died in 187 1, and was buried in 
Westminster Abbey, but never will those who knew him 
forget the beautiful truth-loving spirit which breathed in 
every word he wrote or spoke. 

Discovery of the Paths along which Meteors travel, 
and the Agreement of two of these with the Orbits of 
Returning Comets, 1862. — We must now turn to a most 
interesting discovery made within the last twenty years, 
which proves that our solar system does not consist merely 



ch. xxxii. METEORS. 3°7 

of the sun and the planets, with their satellites, but that 
myriads of smaller bodies are also moving in large orbits 
around our sun. Every one has heard of falling or shoot- 
ing stars, and most people have probably seen one or more 
of these bright meteors rush across the sky on a calm 
summer evening, and then vanish as suddenly as it ap- 
peared. The rude Lithuanian peasants have a touching 
legend about these falling stars. 'To every new-born 
child,' they say, ' there is attached an invisible thread, and 
this thread ends in a star ; when that child dies the thread 
breaks, and the light of the star is quenched as it falls to 
the earth.' Science has taught us a different, but a not less 
wonderful history. It is now known that these meteors are 
solid stones, 'pocket planets' as Humboldt called them, 
which form long elliptical rings round the sun, many of 
which cross our orbit in various directions. When we pass 
through one of these rings, the stones rush through our 
atmosphere so fast that they become heated, and give out 
light for a short time, till they disperse into fine dust and 
vanish. When they are too large to be consumed before 
they reach the earth, they fall, often with great violence, and 
are split into countless fragments. A large collection of 
these meteoric stones is to be seen in the British Museum, 
some weighing hundreds of pounds, others only a few grains. 
They have been analysed, and are found to be composed 
chiefly of iron, tin, sulphur, phosphorus, carbon, and oxygen. 
Before the present century all that was known about 
these bodies was very vague and unsatisfactory. From time 
to time accounts of stone-falls came from different parts of 
the world, but they were not much attended to, and people 
found it difficult to believe that stones and mineral masses 
actually fell from the sky on to the earth. But in 1803 a 
fiery globe was seen to rush over the town of Aigle, in Nor- 
15 



308 NINETEENTH CENTURY. pt. III. 

mandy, and a stony mass was dashed to the ground and 
shattered into thousands of fragments, some of which weighed 
as much as 17^- lbs. This created so much astonishment 
that the French Government sent M. Biot, a celebrated 
French chemist, to examine into the matter, and he reported 
that there could be no doubt of a shower of hot stones 
having fallen upon the earth. 

From this time more interest was taken in meteors and 
meteoric stones. People had remarked for a long time that 
shooting-stars were more abundant from the 9th to the nth 
of August than at other times, and more lately it was also 
noticed that a shower of the same kind happens about the 
13th of November. Astronomers began, therefore, to think 
that these meteors must move in regular orbits, crossing 
the orbit of our earth in certain places, so that we pass 
through them. There were also reasons for thinking that 
the November meteors travelled in an enormous ellipse, 
passing at one end even outside the planet Uranus. 

It was not, however, till thirteen years ago that anything 
was really known. In the year 1862 an Italian astronomer 
named Schiaparelli made a very remarkable suggestion. 
He noticed that a comet which was seen in that year crossed 
the earth's path just at the point where we are always in 
the middle of the meteor-shower on August 10, and it oc- 
curred to him whether it might not be possible that the 
August meteors were travelling in the same orbit as the 
comet. His suggestion turned out to be correct, and by a 
calculation which we cannot follow here, he proved that the 
comet and the August meteors travel along precisely the same 
path in the shape of a long ellipse passing at one end out- 
side the planet Neptune, the most distant of the known 
planets. This was the first time that the orbit of any set 
of meteors had been traced out. 



ch. xxxii. METEOR-SHOWERS. 309 

The next was that of the November meteors, which was 
determined by Adams, and also independently by Leverrier. 
It had been shown by searching out all the past accounts 
of November showers that in times gone by the earth passed 
through these meteors a little earlier in the year than she 
does now, and this could not be accounted for by any irre- 
gularity in the movement of the earth. It looked therefore 
as if the orbit of the November meteors must be slowly 
shifting, just as the orbits of the planets do, within certain 
limits. It was upon this shifting that Adams founded his 
calculations, and he worked out the meteor path with great 
accuracy, showing that those astronomers had been right 
who thought it extended beyond Uranus. This time the 
problem was solved by pure astronomical reasoning, but per- 
haps the most remarkable part of the story is that in 1866, 
long after Adams had determined the orbit, a new comet 
was seen, which was found to move exactly along the path 
of the November meteors, in the same way that the comet 
of 1862 agrees with those which fall in August. 

Although these two meteor-showers are the most import- 
ant, they are by no means the only ones crossed by our 
earth. Mr. Proctor states that on any clear night, if you 
watch carefully, you may see about six shooting-stars in one 
hour; and Professor Newton, of America, has calculated 
that 7,500,000 meteors large enough to be seen without a 
telescope pass through our atmosphere in one single day 
and night. At least a hundred sets of meteors, or meteor- 
systems as they are called, are known to astronomers, and 
each one of these is composed of millions of bodies ; and 
you must bear in mind that these systems do not move 
round us, but round the sun, so that it is only because we 
happen to cross their path that we know anything of them. 
It would be idle to suppose that these hundred meteor- 



3io NINETEENTH CENTURY. pt. hi. 

systems which we come across are the only ones existing. 
On the contrary, we have every reason to think that they 
are only a few out of thousands of meteor-systems which we 
never meet, and which probably grow more numerous the 
nearer they approach the sun. 

And so we arrive at the wonderful thought that the 
whole of our solar system is swarming with meteors col- 
lected into more or less defined rings and rushing along with 
immense speed in their motion round the sun. What their 
use is we do not know. Some astronomers have imagined 
that the heat of the sun is kept up by these meteoric stones 
falling in countless myriads on his face, but this is disputed 
by others ; and for the present it is enough if we can picture 
to ourselves these rings of meteors whirling round and round 
in space, and flashing into light as they rush through our 
atmosphere whenever we happen to cross their path. 

Use of Improved Telescopes in Discovery of New 
Heavenly Bodies. — In truth, astronomy has during the 
last twenty years advanced so rapidly along different lines 
that we cannot follow them in a general history. The 
improvement in telescopes alone has made many observa- 
tions possible which before were not so. Instead of rough 
instruments, constructed under great difficulties like the 
telescopes of Galileo and Sir W. Herschel, magnificent 
refracting telescopes, with large achromatic lenses, are 
now found in all good Observatories. The finest re- 
fracting telescope in the world is that of the United Stales 
Naval Observatory, Washington, with an aperture of twenty- 
six inches, while one still larger is being constructed for the 
Vienna Observatory. The finest reflecting telescopes are 
Lord Rosse's, of a six-foot aperture, and that of the Mel- 
bourne Observatory, Australia, of a four-foot aperture, and 
the Lick telescope in California. 



ch. xxxn. ADVANCES IN ASTRONOMY. 3" 

Again, self-registering instruments are now at work in 
every part of the world, recording events at every instant 
with unvarying accuracy. Clockwork regulates the move- 
ments of the telescope itself, while microscopes enable the 
observer to read off the most delicate measurements. And, 
what is of still greater importance, photography enables 
us to obtain permanent records of passing astronomical 
phenomena. Thus photographs were taken of the ingress 
and egress of Venus during the late transits, and though 
these were imperfect, yet there is little doubt that such 
attempts will be successful in the end, and hourly photo- 
graphs are now being taken of the sun whenever it is 
visible. 

With all these appliances many features of the heavenly 
bodies are observable which were before indistinct. On the 
nights of August n and 17, 1877, Professor Asaph Hall dis- 
covered with the Washington telescope two of the smallest 
heavenly bodies (meteorites excepted) which have ever 
yet been seen. These are two satellites revolving round 
the planet Mars. It is difficult to be certain how large 
they are : the one which is farther from the planet is 
the smaller, measuring probably, according to Professor 
Pickering, about six miles across, and it moves round 
Mars in 30 hours 17 minutes 53 seconds. The inner 
one is brighter, and measures probably about seven miles 
across; its period of revolution is 7 hours 3% minutes. 
These two satellites are named Deimos and Phobos, or Fright 
and Flight, because Homer makes these attendants upon the 
God of Battle. They are so near to Mars that if there be 
living beings on that planet with eyes and telescopes like 
ours, they will be able to tell whether their moons are in- 
habited, for the inner one is only 4000 miles distant, or 
sixty times nearer Mars than our Moon is to us. 



312 NINETEENTH CENTURY. pt. in. 

Another important discovery, believed on good grounds 
to have been made within the last few years, is that of one, 
and perhaps two, planets revolving between Mercury and the 
sun. We shall see presently that Leverrier's analysis of the 
planetary orbits points to a probability that some bodies of 
this kind exist nearer to the sun than Mercury, and in 1859 
a French physician, M. Lescarbault, asserted that he had 
seen a round body crossing the sun's disc which Leverrier 
believed to be a planet, and called by the name of Vulcan. 
During the eclipse of the sun on July 29, 1878, Professor 
Watson of the Observatory of Michigan devoted all his 
attention to a search for this planet, and though he did not 
find it, he saw two other bodies which he believes to be 
planets, but whose positions do not either of them agree 
with that of Lescarbault's Vulcan, so that if future observa- 
tion confirms these discoveries we should know of three 
intermercurial planets. 

Leverrier's Analysis of the Orbits of the Planets, 
1875. — Thus far it has been the gradual perfection of 
instruments, and the use of them in patient research, which 
has given us our vantage ground. But meanwhile the 
great mathematical minds have not been idle in demon- 
strating that ' order is heaven's first law,' and after thirty-six 
years of constant labour M. Leverrier has completed the 
analysis of the movements of the eight large planets, so 
that the student of astronomy has now before him a chart 
by which he can check the actual revolutions in our 
planetary system for two thousand years to come. It is 
impossible for any but mathematicians properly to ap- 
preciate this work, but we may form some idea of it by 
picturing to ourselves the problem which Leverrier had to 
solve. 

We must first of all remember the fact proved by New- 



ch. xxxil. LEVERRIER'S ANALYSIS. 313 

ton (see p. 148), that not only does the sun attract the 
planets, and the planets the sun, but that every planet 
attracts every other planet in the solar system. Now, as 
no two planets revolve round the sun in the same time, 
they are constantly changing their positions with regard to 
each other, just as, for example, the short and long hands 
of a clock are sometimes near together and sometimes far 
apart : only in the case of the planets it is as if there were 
eight hands moving, all at different rates, and these rates do 
not bear an even proportion to each other. Moreover, the 
planets do not move all upon one flat surface, like the face 
of a clock, but their orbits are in various planes, and these 
planes themselves are subject to irregular motions. Lastly, 
each planet moves in an ellipse, and these ellipses vary in 
different ways. From this it arises that the planets cross 
each other's paths at very varying intervals, and are inces- 
santly assuming different positions with regard to each other. 
Now, as the attraction of two bodies becomes stronger as 
they approach each other, it is clear that as the positions of 
the planets vary, their mutual attractions vary too, and the 
task which Leverrier set himself was, to calculate all these 
attractions and thus to discover the mass of each planet 
by the effect which it has upon the other planets, and the 
effect they have upon it. 

As our earth is one of the planets, the first thing was to 
find out by the appare7it motion of the sun, what is the real 
path of our earth and how it is affected by all the others, 
and from this to go on to each of the planets in turn. But 
it must be remembered that no two planets can be studied 
as if they were alone in the heavens ; on the contrary, they 
are never free from the attractions of all the other six, whose 
positions are constantly changing, so that the movements cross 
and re-cross each other like the waves of a troubled sea. 



3H NINETEENTH CENTURY. pt. hi. 

In order to disentangle this complicated series of changes, 
it was necessary to gather together all the observations made 
of the positions of each planet from the earliest ages, and 
to combine the whole mathematically into one complete 
theory, in which all the movements should be truly and 
accurately accounted for. This Leverrier undertook, and 
it was in the course of his work that he found some move- 
ments of Saturn and Uranus which were not produced by 
any of the known planets, and he was thus able to announce 
the existence of the planet Neptune (see p. 304). He next 
found that Mars and Mercury were pulled out of their path 
by some matter for which he could not account. As far as 
Mars is concerned, this matter proved to be upon our earth, 
whose mass had been reckoned too low, but in the case of 
Mercury the cause is not yet certain, although the supposed 
planet of Lescarbault and the two small bodies observed by 
Watson may probably help to explain the irregularity. 

With these and a few other trifling exceptions, Leverrier 
succeeded in 1874 in completing his gigantic task, and in 
computing the position of the four most distant planets, 
Jupiter, Saturn, Uranus, and Neptune, for a period of 2000 
years from 1880 at intervals of 500 years, so that future 
astronomers will be able to calculate at the periods 2350, 
2850, 3350, and 3850, whether the movements of the 
planets have followed the same order as in times past, or 
whether any disturbing influence has arisen. 

Chief Works consulted. — Airy's 'Report on Astronomy,' British 
Association, 1883 ; J. D. Forbes's ' Progress of Mathematical and 
Physical Science' — Sixth Dissertation; 'Encyclopaedia Britannica,' 
new edition ; Guillemin, 'The Heavens;' Herschel's 'Astronomy;' 
Grant's ' Physical Astronomy ; ' ' Reports of the Astronomical Society ; ' 
' The Orbs of Heaven,' Mitchell ; Proctor, ' On Shooting-Stars and 
Meteors;' Miss Gierke, 'Astronomy of the Nineteenth Century,' 1886. 



CH. xxxiii. INTERFERENCE OF LIGHT. 3*5 



CHAPTER XXXIII. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Dr. Young explains the Interference of Light — Malus discovers the 
Polarization of Light caused by Reflection — Fresnel — Polarization 
of Light explained by Young and Fresnel — Sir David Brewster and 
M. Biot on colours produced by Polarization — Fizeau — Foucault — 
Velocity of Light — Colour Theory of Young and Helmholtz. 

We must now go back to the history of Light, which we 
left, as you will remember, at the end of the seventeenth 
century, at the point which Newton and Huyghens had 
reached. During the whole of the eighteenth century very 
little was learnt about this science, and it remained for the 
men of our own time to make the next step and to discover 
the grand laws of light which we must now consider. It 
will be best to divide our subject into two parts — ist. The 
discoveries which have led to a true Theory of Light. These 
are very difficult to understand, and you must not expect 
to gain more than a slight notion of them ; 2d. The new 
facts lately discovered about the Chemistry of Light, and 
called Spectrum Analysis, and of these I hope you may 
understand enough to fill you with delight at the beautiful 
histories they reveal. 

Discovery of the Interference of Light by Young, 
1801. — You will remember that Newton and Huyghens had 
proposed two different theories of light (see page 174). 



3 i6 NINETEENTH CENTURY. pt. in. 

Newton's, called the Corpuscular or Emission Theory, sup- 
posed light to be made of minute particles darting out from 
the sun and every light-giving body. Huyghens, on the con- 
trary, taught that light is produced by the vibrations or 
waves of an invisible ether which is supposed to fill all space. 
This was called the Undulatory or Wave Theory. 

Newton's authority was so great, and the experiments he 
made to prove his theory were so striking, that the l Corpus- 
cular theory ' was generally received as the true one, espe- 
cially as Huyghens had only made a few simple experiments 
in support of his idea ; and it was more than a hundred 
years after Huyghens first published his 'Treatise on Light' 
before a man arose to defend the Undulatory theory and to 
bring it again into notice. This man was Dr. Thomas 
Young, the first Professor of Natural Philosophy at the 
Royal Institution of London. 

Thomas Young, who was the son of a Quaker, was born 
at Milverton, in Somersetshire, in 1773, and died in 1829. 
He was brought up at home, and seems to have been a very 
clever lad, for he knew seven languages at the age of four- 
teen, besides having studied Natural Science as an amuse- 
ment. He then went to the Edinburgh University, where 
he worked under dear old Dr. Black, whose enthusiasm, no 
doubt, helped much to increase his love of science. When 
he was only twenty he sent a paper on 'Vision' to the Royal 
Society, and was elected a member the following year. He 
then went to Cambridge in order to be able to satisfy the 
College of Physicians, and practised as a medical man in 
London, where, in 1 801, he was also made Professor of 
Natural Philosophy at the Royal Institution, which had just 
been founded, and Editor of the Nautical Almanack. He 
is very famous as one of the first men who deciphered the 
Egyptian hieroglyphical writings, and you will often hear 



ch. xxxiii. DR. THOMAS YOUNG. 317 

him mentioned as an Egyptian scholar ; but what we have 
now to consider are his discoveries about Light. 

Young tells us himself that it was in May 1801 that he 
first made an experiment which seemed to him to prove 
that light must be a succession of tiny waves moving across 
space as Huyghens had supposed. His experiment was the 
following. He made a hole in the window-shutter of a dark 
room, and covered it with a piece of thick paper, in which 
he had pricked a small hole with a needle. He then put a 
small looking-glass outside the shutter, so as to throw the 
sunlight very fully upon the hole and send a cone of spread- 
ing light through it. In this cone of light he held a very 
narrow strip of card and watched the shadow which it threw 
on the wall, or on another piece of card behind it. On each 
side of the shadow there were some faint fringes of colour, 
but besides these he saw in the shadow itself dark and light 
upright tinted bands, which finished off in a faint white band 
in the middle of the shadow. It was from these faint bands, 
which many men would have thought not worth noticing, 
that Young worked out the truth of the Wave Theory of 
Light. 

The first question he asked himself was — * Why should 
there be any light at all in the shadow?' This was not 
difficult to answer, for as light travels in all directions, a part 
of it, passing on each side of the strip of card, will spread 
out behind it. But why should this light arrange itself in 
stripes and not fall equally all over the shadow? It seemed 
at first impossible to explain this ; but when Young placed 
his hand so as to prevent the light passing along one of the 
edges of the card he found that the fringes or bands dis- 
appeared entirely i and when he took away his hand they re- 
turned. It was clear, then, that so long as the light passed 
in one direction only behind the card it spread itself out 



3i8 NINETEENTH CENTURY, pt. hi. 

equally, but directly the two sets of rays from the two sides 
met each other, dark and light bands appeared. 

Now Newton's emission theory could give no explana- 
tion of this curious fact, for if light were made of tiny par- 
ticles there is no reason why these particles, in crossing each 
other, should make dark bands. On the contrary, the more 
of them there were the more light there ought to be. The 
Undulatory or Wave Theory, however, explained the bands 
perfectly, and this we must now try to understand. 

You will remember that Huyghens supposed an ether 
filling all space to be set in motion by the sun, or any other 
luminous body, and to heave up and down in tiny waves, just 
as the sea heaves, or the water of a pond, when you agitate it. 

Suppose, therefore, that a number of waves of water, all 
of the same size, are moving along one side of a lake as at a, 
Fig- 57, p. 315, and flowing out through a narrow channel at 
the end, and suppose another set of waves to be moving along 
the other side, b, so that the two sets meet at the mouth of 
the channel. Then, if the two waves c and d are both rising 
up when they meet, they will join together into one large 
wave, and will continue to flow in large waves down the 
channel. But if they meet, as in Fig. 58, when c is falling 
and d is rising, then c will flow into the hollow of d and fill 
it up, and instead of a large wave being made, the surface 
of the water will soon become smooth. 

Now Young pointed out that this is exactly what happens 
to the undulations of light. After passing through the hole 
in the shutter, they move on till they come to the card, and 
here they wheel round each edge of the card and meet 
behind it. Those which meet in the middle of the shadow 
have each travelled exactly the same distance with the same 
number of waves, so they meet as in Fig. 57, and a strong 
undulation is produced, causing a band of light. But on 



CH. XXXIII. 



INTERFERENCE OF LIGHT. 



319 



either side of the exact middle the rays will not have tra- 
velled exactly the same distance, but one will have made 
half a wave more than the other, so they will meet as in Fig. 
58, and destroy each other, causing a band of darkness. 
Outside these again the ray which has come the longer dis- 
tance has had time to make up another half-wave, so it meets 
the other ray as a friend again, and both of them rising 
together, a strong wave and a light band is the result. In 




Fig. 57. 




Fig. 58. 

Diagrams illustrating the Interference of Waves. 

In Fig. 57 the waves, c d, meet in the same phase, and produce strong undulations. 
In Fig. 58 the waves, c d, meet in the opposite phase, and interfere with each 
other. 

this way they go on, first helping and then interfering with 
each other, and thus making alternate bands across the 
shadow. For this reason Young called his discovery the 
1 Interference of light? 

If this experiment is made with light of one colour only, 
as, for example, with light which has been passed through 
red glass, and so is composed only of red rays, then the 
bands are simply black and red. But if sunlight is used, 



320 NINETEENTH CENTURY. pt. in. 

another curious effect is seen, namely, a succession of bands 
appear tinged with the colours of the rainbow ; and this, too, 
Young showed to be beautifully explained by the Undula- 
tory Theory. It was stated at p. 177 that the colour of 
the light which reaches our eye depends upon the rapidity 
of the vibrations of the ether, just as the sound of a note 
upon our ear depends upon the rapidity of the vibrations of 
the air. Consequently the waves of the prismatic colours 
are of different lengths, so that when the two rays of light 
meet behind the card the waves of the various colours do 
not all arrive together. For example, those waves which 
cause us to see the colour violet are much shorter and more 
rapid than those which cause us to see red. Therefore, 
when the red waves meet each other as friends (as in 
Fig. 57), and make a strong vibration, the violet ones will 
meet each other as foes (as in Fig. 58), and interfere with 
each other ; and so we shall see a bright red stripe made by 
the strong red wave, while the violet waves will be destroyed. 
A little farther on the violet waves will meet as friends, and 
then we see a violet streak, while the red ones will in their 
turn be destroyed. 

Colours on the Soap-bubble. — The beautiful colours 
of the soap-bubble are caused in this way, and an explana- 
tion of them will help you to picture to yourself this effect 
of the interference of light. If you have ever blown a well- 
shaped soap-bubble, and watched it settle down quietly 
where there is no wind to disturb it, you cannot fail to have 
noticed the colours which appear upon it. If the bubble is 
very perfect, these colours arrange themselves in rings, 
beginning with a dark spot at the top of the bubble and 
forming alternate bands of blue, yellow, orange, and red, 
which grow fainter and fainter down the sides of the bubble 
till they disappear. The reason of these colours is that, 



ch. xxxiir. COLOURS CAUSED BY INTERFERENCE. 321 



when the sunlight falls on the thin film of the bubble, a 
little of the light is reflected straight back to the eye from 
the surface #, Fig. 5 9 ; but most of it passes on to the 
second surface b, and there again some is reflected, so that 
two sets of waves are constantly reaching the eye, one from 
a and one from b. These two sets meet before they come 
to our eye, and we have just seen that it depends entirely 
how they meet what colour we see. 

- Suppose the film is just thick enough for the two rays 




Fig. 59. 
Reflection of Light from the two surfaces of a Soap- bubble.* 

r, Ray of light, part of which is reflected from the surface a, and part from the 
inner surface, b, to the eye. 

to meet when the red waves of each are rising ; we shall 
then have a full red wave upon our eye. But in that case, 
as the violet waves are a different length, they will not have 
met as friends, but as foes, one up and the other down, and 
will destroy each other ; and so will the waves of all the 
other colours, because they are not of the same length as 
the red waves. Therefore the only impression on our eye 

1 The film of a soap-bubble is really only the thickness of a fine 
line even in the thickest part ; but it was necessary to exaggerate the 
two surfaces in the diagram to show the passage of the ray of light. 



322 NINETEENTH CENTURY. ft. hi. 

will be that of red. But the bubble is always growing 
gradually thicker down its sides because the soapy liquid is 
creeping downwards. So a little lower down the red waves 
from the two surfaces a and b will no longer fit each other, 
but will meet unevenly and the red colour will be destroyed. 
It will now be the turn of the violet rays to combine and 
make a strong wave to our eye ; a little lower down it will 
be the turn of the green waves, then of the yellow, and then 
the film will be thick enough for the red waves to come 
together again, and so it will go on ; each colour in its 
turn will produce a strong wave, while all the others are 
quenched, until the film is too thick for the effect to be 
produced. 

This is a very rough idea of the way in which the Undu- 
latory Theory explains the colours which we see in shadows 
and in the soap-bubble. When you study the subject of 
light you will see how very complicated these wave move- 
ments really are ; but without special knowledge you cannot 
understand more than I have given you here. The colours 
on mother-of-pearl, on a duck's neck, on the transparent 
wings of insects, and even on the scum floating on a pond, 
are all produced by the interference of light, and we owe 
the discovery of this simple and beautiful explanation to 
Dr. Thomas Young. 

Malus discovers trie Polarization of Light by Re- 
flection, 1808. — The next step in the science of light was 
made by Etienne Louis Malus, a young French engineer 
officer, who was born in 1775, and died in 181 2, when he 
was only thirty-seven years of age. He was a most accom- 
plished mathematician, and if he had lived longer, would 
probably have been one of the most celebrated men of our 
century. 

You will remember that in 1669a Danish physician named 



ch. xxxiii. MALUS ON POLARIZATION. 323 

Bartholinus discovered that a ray of light is split into two 
rays in passing through Iceland spar in any direction except 
along the axis of the crystal ; and that Huyghens explained 
this by saying that the crystal was more elastic in one direc- 
tion than in another, so that the waves moved at different 
rates through it (see p. 179). To understand Malus's dis- 
covery you must also remember that one of these divided 
rays, if it falls upon a second crystal in the same manner as 
the first, goes on its way as a single ray, but if the second 
crystal is turned round a little the ray splits up again into 
two rays. 

In the year 1808, M. Malus was standing at his study 
window in the Rue d'Enfer, in Paris, looking through a 
prism of Iceland spar at the sunlight reflected from the 
windows of the Luxembourg Palace, which stood opposite. 
All at once he observed to his surprise that he saw only one 
image through the prism instead of two. Turning his prism 
a little, he got the two images again, but one was much 
brighter than the other, and when he turned the crystal a 
little farther the other image disappeared, and he had only 
one again. * In fact, the light which was reflected from the 
window at one particular angle (5 6° 45') behaved just like 
one of the divided rays which has come out of a crystal, and 
not like an ordinary ray which comes from the sun. 

This remarkable peculiarity puzzled Malus greatly, and 
led him to make a great many experiments, by which he 
discovered that, whenever light is reflected from glass at this 
particular angle of 5 6° 45V it has the peculiar characters of 
a divided ray which has passed through Iceland spar. Light 
reflected from other substances is also divided up in this 
way, only the angle at which this change takes place is dif- 

1 The polarizing angle of glass varies between 45 35' and 58 , accord- 
ing to the nature of the glass. 



324 NINETEENTH CENTURY. ft. hi 



ferent for each different substance. Malus was the first 
to call this peculiar effect polarization, and light which 
behaves in this way has since been always called ' polarized 
Kght.' 

His discovery led to a completely new study, for people 
had almost forgotten the experiments which had been made 
by Huyghens more than ioo years before; but this novel 
and curious fact attracted attention, and the subject was 
taken up again. Malus did not live to explain the matter; 
he found out many remarkable facts about it, but it was 
Young and the French philosopher Fresnel, who really 
worked out the theory of the polarization of light. 

Polarization of Light explained by Young and 
Fresnel, 1816. — Augustin Fresnel, the contemporary and 
friend of Thomas Young, was born at Broglie, in France, in 
1788. He was a delicate backward boy, who disliked 
books, but loved practical experiments, and he followed his 
tastes by becoming an engineer. Being a Royalist, how- 
ever, he was harshly treated by the Emperor Napoleon I., 
and he retired to Normandy to devote himself to science. 
He died of consumption in 1827. 

It is very difficult to decide whether Young or Fresnel 
was the first to point out how certain peculiar vibrations of 
the ether explain the polarization of light. But fortunately 
this need not trouble us, for the men themselves were not 
anxious to dispute about their claims. Young's discoveries 
were very coldly received in England, for very few men un- 
derstood them; and unfortunately Lord Brougham wrote 
some severe articles against them in the 'Edinburgh Re- 
view,' which made people think they were only foolish 
speculations. But in France two men, Fresnel and his 
friend M. Arago, understood and valued Young's labours 
as soon as they heard of them, and from that time the three 



ch. xxxiii. THE POLARIZATION OF LIGHT. 325 

men helped each other in every way without the least 
jealousy as to who should have the credit of the work. 

Fresnel had puzzled out the question of the ' Interference 
of Light ' before he heard that Young had done so too ; and 
it happened that while Fresnel and Arago were one day 
making experiments upon the way in which waves of light 
interfere with each other, they found that the ordinary and 
extraordinary rays which come out of a piece of Iceland spar 
cannot be made to interfere with or quench each other, as 
may happen in the case of two ordinary rays. (See p. 315.) 
This led Fresnel to suspect that the waves in the two rays 
must move in a different manner. He wrote this to Dr. 
Young, and found that he also had the same idea ; and this 
led to a number of experiments, by which they proved at last 
that a natural ray of light is not composed merely of upright 
waves as in a, Fig. 60, p. 322, but also of waves from side 
to side as in b, and others at every angle between these two, 
so that the ray is really round and not flat ; when light is 
polarized, this complex vibration is destroyed, and the 
waves of each ray move only in one plane. 

To understand this, take a piece of string, and, fastening 
one end to the wall, hold the other end in your hand. If 
you now move your hand up and down, you will make 
waves in the string which will point up to the ceiling and 
down to the ground, making what are called vertical vibra- 
tions (a, Fig. 60). Stop this movement, and then move 
your hand from side to side; the waves will now point 
from wall to wall in horizontal vibrations (b, Fig. 60). If 
you then move your hand so that it points to the ceiling 
to your right, and the floor to your left, you get waves 
between the two others, and so you can go on varying the 
position of the waves in all directions ; or, in scientific lan- 
guage, you cause the string to vibrate i?i different planes. 



326 



NINETEENTH CENTURY. 



PT. III. 



Now Young and Fresnel proved that a natural ray of 
light is composed of all these different waves moving at the 
same time, some up and down, some from side to side, and 
some between the two. But when the light passes through 
a piece of Iceland spar, there are two and only two ways in 
which the waves can move : one up and down — and along 
this path one ray of light goes ; the other from side to side 
at right angles to the first — and along this the other ray goes 
at a different speed, and so they become divided. 

You can imitate this by passing your string through a 
card with a straight slit in it. Place the card upright, as 
at a, Fig. 60, and it is clear that the waves will be up and 




Fig. 60. 

Diagram illustrating the passage of Waves of Light through a crystal. 

A, Waves moving in a vertical plane, b, Waves moving in a horizontal plane. 

down ; place it sideways, as at b, and the waves will be from 
side to side. These two positions of the card imitate the 
two paths of a ray of light through a crystal, and they show 
how the difference in the peculiarities of the divided rays is 
caused by their moving in a different plane. 

We cannot follow this out more completely in a history, 
for the polarization of light is a very difficult subject ; but 
this was the first step made in it. Fresnel afterwards 
worked out accurately why, when light is reflected at a 
certain ande, the vibrations are all made to move in one 



ch. xxxiii. VELOCITY OF LIGHT. 3*7 

plane, and so the light is polarized, as Malus had found it 
to be from the surface of the Luxembourg windows. He 
also showed how in some crystals, as in quartz crystals, the 
waves are made to act upon each other, so that, instead of 
moving to and fro, they wind round and round like the wire 
of a corkscrew. These and many other experiments, as, for 
example, those upon the beautiful colours caused by polar- 
ization, were carried much farther by the eminent French 
chemist, M. Biot (born 1774, died 1862), and by Sir David 
Brewster (born 1784, died 1868), but they are too long and 
difficult to be explained here. As I said at the beginning 
of this chapter, the ' Theory of Light ' requires a special 
study, and if you have understood something of the move- 
ment of the supposed ether waves — how they can interfere 
with each other and produce light or darkness, how they 
produce coloured rings in the soap-bubble, and how their 
vibrations are altered in passing through a crystal or in re- 
flection at certain angles — you have learnt as much as can 
be easily grasped of the discoveries of Young and Fresnel. 

Velocity of Light in Air and Water— Fizeau— 
Foucault. — -It is necessary, however, to mention here one 
strong proof of the wave-theory of light although the detailed 
experiments are too complicated to understand without long 
explanation. M. Fizeau and M. Leon Foucault, eminent 
French physicists, have invented two different methods by 
which the velocity of light can be accurately measured. M. 
Fizeau's depends upon the rotation of a toothed wheel behind 
a slit which cuts off a reflected ray, or allows it to pass, accord- 
ing to the rate at which the wheel is turned. M. Foucault's 
depends on the rotation of a small mirror revolving round 
an axis in its own plane like a coin upon its edge, by means 
of which the spot of light from a ray changes its position 
perceptibly in the minute interval of time occupied by the 



328 NINETEENTH CENTURY. pt. hi. 

reflection of the ray. By means of these methods it is 
possible to measure very accurately how long a ray of light 
takes in passing through any medium. Now, if Newton's 
* Corpuscular Theory ' had been true, a ray ought to pass 
more rapidly through water than through air, but on the 
Undulatory Theory the opposite should be the case. MM. 
Fizeau and Foucalt have, however, found that light will 
travel four miles in air in the time that it will only travel 
three miles in water, thus giving almost demonstrative 
proof that the undulatory theory of light is the true one. 

Colour Theory of Young and Helmholtz, 1801-1856. 
— We must now return to Dr. Young, for it was he who 
first suggested the theory of the cause of colours being 
distinguished by the eye, although this theory was neglected 
until Professor Helmholtz worked it out more fully in our 
day. Young suggested that there are three kinds of nerve- 



fibre in the retina of our eyes, one of which is most strongly 
affected by the long waves of light producing the sensation 
called red, another affected by the medium waves producing 
green, 1 and the third affected by the shortest waves producing 
violet Each of these sets of nerves would, however, be 
slightly excited by the other waves as well, and so the 

1 Green, not yellow, as was formerly supposed. The study of 
coloured light has shown that, so far as we can distinguish, there are 
three primary colours ; these are red, green, and violet, for the yellow 
of the spectrum is produced by a mixture of red and green. It is only 
in paints or pigments that an effect of green is produced by the mixture 
of blue and yellow. 



ch. xxxiii. VELOCITY OF LIGHT. 329 

different sensations would overlap and blend to produce 
the gradual tints of the spectrum. This theory has now- 
been most perfectly worked out by Professor Helmholtz, 
and the diagram, Fig. 60 a, shows by three curves the 
amount of excitement supposed to be produced on the 
three kinds of nerve-fibre. Thus the curve R shows how 
the left end of the spectrum affects the red nerve-fibres 
most strongly, while yet some effect is produced for almost 
the whole length ; while in the same way the green and 
violet nerve-fibres have each their own maximum of excite- 
ment. An equal stimulation of all the fibres, such as is 
produced by an ordinary ray of light, gives a sensation of 
white. This explanation was most curiously confirmed by 
results obtained by Clerk-Maxwell in colour-blindness, for 
he showed that it is exactly one of these three primary 
colours, generally red, that people affected with colour- 
blindness are unable to distinguish. They see only two 
colours and their combinations, which suggests that the 
nerve -fibres answering to the third colour are weak or 
deficient. 



Chief Works consulted. — Young's ' Lectures on Natural Philosophy,' 
1845; Peacock's 'Life and Works of Young;' Arago's ' Eloge of 
Fresnel ; ' Herschel's * Lectures on Familiar Subjects ; ' Tyndall, ' On 
Light ; ' Spottiswoode's ' Polarization of Light ; ' Whewell's ' Inductive 
Sciences ; ' Helmholtz, ' Physiologische Optik ' and Popular Scientific 
Lectures. 



330 XIXETEEXTH CEXTURY. pt. hi. 



CHAPTER XXXIV. 

SCIENCE OF THE NINETEENTH CEXTURY (CONTINUED). 

Spectrum Analysis and its Applications to Terrestrial and 
Celestial Bodies — Celestial Photography. 

History of Spectrum Analysis, 1800-1861. — "We now 
come to the history of Spectrum analysis, or the study of 
the various coloured bands produced by different kinds of 
light when seen through a prism. This is certainly one of 
the most wonderful discoveries of our century, and though 
its history is difficult, partly because it belongs to our own 
time and is going on even now. yet we may learn something 
about it The first step was made, as you will remember, 
when Newton discovered that white light is composed of 
different coloured rays, but even he little suspected what 
histories those rays could be made to tell. 

Discovery of Heat-rays by Sir William Herschel, 
1800. — One of the first facts which was learnt in this cen- 
tury about the spectrum was, that the coloured band which 
is seen when a ray of white light is passed through a prism 
does not give us the whole of the dispersed ray ; for there 
are many invisible rays at both ends of the coloured part 
which are very active, though we cannot see them. 

It had always been thought that the hottest rays must 
be those, such as the yellow ones, which give the most light, 
and in the year 1800 Sir William Herschel, wishing to try 



ch. xxxiv. SPECTRUM ANALYSIS. 331 

this, took a thermometer and passed it gradually from one 
end to the other of the coloured band. The result was 
curious. He began at the violet end of the spectrum (Plate 
I. No. 1, p. 330), and, as he expected, the thermometer rose 
higher and higher as he approached the yellow part ; but 
to his surprise it did no! stop here. When he passed on 
through the yellow into the red, the heat still increased, 
and even became more intense as he passed out of the 
coloured band altogether into the darkness beyond. By 
this experiment he found that the heat-rays extend for some 
distance beyond the red colour, and that they are strongest 
in that part where no light is to be seen. 

Discovery of Chemical Rays by Hitter, 1801. — 
Soon after Sir William Herschel had discovered the dark 
heat-rays, a still more remarkable fact was brought to light 
about the violet end of the spectrum. The Danish chemist 
Scheele, whom you will remember as one of the discoverers 
of oxygen (see p. 230), had once remarked that nitrate of 
silver will turn black if the violet rays of a spectrum are 
thrown upon it. In 180 1 Professor Ritter, of Jena, was 
repeating this experiment, and he found that the black 
patches appeared slightly on those parts of the paper where 
the violet rays fell, but very strongly indeed beyond those 
rays where the spectrum was quite dark. So that at this 
end also there are invisible rays, and these have the extra- 
ordinary power of decomposing or breaking up nitrate of 
silver, and some other substances, so as to leave distinct 
marks upon anything touched by them. 

Photography. — You will see at once that this is the 
secret of Photography. In 1802, Sir Humphry Davy and 
Dr. Thomas Wedgwood suggested that pictures might be 
taken in this way by the rays of the sun acting upon chloride 
of silver, and they even succeeded in making some. But 
16 



A 



332 NINETEENTH CENTURY. PT. hi. 

they could not prevent them from fading away again, and 
it was not until 1839 that a Frenchman named Daguerre 
learnt how to fix the pictures so that they would remain, 

Photography is now chiefly worked with dry plates, but 
the old wet process will best illustrate how the rays of light 
produce a picture. In this process the glass plate which 
is to receive the picture has been first covered with a thin 
film of collodion (that is gun cotton dissolved in ether and 
alcohol) mixed with finely powdered iodide of potassium. 
The plate is then bathed in a solution of nitrate of silver, 
and a chemical reaction takes place which leaves a film of 
iodide of silver on the surface. When the rays of sunlight 
reflected from your face are brought to a focus on the lens of 
the camera, and fall upon this plate, the chemical rays (which 
are chiefly those beyond the violet end of the spectrum) de- 
compose the iodide of silver; and after some more chemicals 
called protosulphate of iron and pyrogallic acid have been 
poured upon it, the parts which the light has touched all start 
out in different shades, exactly in proportion as the chemical 
waves of light have fallen upon them strongly or feebly. The 
picture will be exactly the opposite to your real appearance, 
because where most light has fallen, there the chemicals 
will be most decomposed and will leave the blackest tints. 

Another fluid called hyposulphite of sodium is next 
poured upon the plate to dissolve away any of the iodide 
of silver which remains undecomposed by the light, so that 
when the sun next falls upon it it may not blacken the rest 
of the plate and destroy the picture. Then the glass plate 
is again placed in the sun with paper under it which has 
been sensitized, that is, impregnated with chloride of 
silver, by being bathed in solutions of nitrate of silver and 
chloride of sodium. Upon this paper the shades will be 
reversed, for under the dark parts of the plate the sun will 



ch. xxxiv. PHOTOGRAPHY* 333 

act feebly on the paper, and produce light patches, while 
through the light parts it will act strongly and produce 
shadows. And in this way the lights and shades of your 
image will appear in their right places on the paper. The 
printed sensitized paper is now bathed in hyposulphite of 
soda, which dissolves off the unaltered chloride of silver, 
leaving the photograph permanently printed in reduced or 
metallic silver. All this work is done by those chemical 
rays which are chiefly at and beyond the violet end of the 
spectrum, and this explains why bright red and yellow objects 
come out dark in a photograph, because these colours con- 
tain so few of those particular chemical rays, while the 
darkest blue and violet come out nearly white, because they 
act strongly upon the nitrate of silver. 

It was formerly thought that the chemical rays of the 
spectrum acted almost entirely at the violet end, but Captain 
Abney has discovered that by using a peculiar film of silver 
bromide, he can produce photographic impressions by rays 
far into the red of the spectrum, showing that the chemical 
action does not so much depend upon peculiar rays as upon 
the sensitiveness of the molecules of certain substances to 
the different rates of vibration in the various parts of the 
spectrum. 

Wollaston first observes the Dark Lines in the 
Spectrum, 1802. — In the same year that Ritter discovered 
the chemical rays at the dark end of the spectrum which 
have given us the whole art of photography, Dr. Wollaston, 
one of our most celebrated chemists (born 1766, died 1828), 
first saw the daik lines in the spectrum which have enabled 
us to discover the actual materials which exist in the sun 
and stars. Dr. Wollaston, who made many good experiments 
on light, was one day examining ordinary daylight through 
a prism, and instead of letting in the light by a round hole 



334 NINETEENTH CENTURY. pt. in. 

or large slit in the shutter as Newton had done, he made 
only a very thin slit, so that the colours of the spectrum 
were prevented from overlapping each other, as they had 
done in Newton's experiment. The result was that seven 
dark upright lines or spaces appeared in the band of colour, 
which seemed to show that no light fell on those parts. 
Wollaston did nothing more than point out the existence o 
these lines ; but in 1 8 1 4 Fraunhofer, a German optician, 
who had heard nothing of Wollaston's experiment, discovered 
them over again independently, and learnt more about them. 

Fraunhofer, 1787-1826. — Joseph Fraunhofer, the son 
of a glazier, was born in 1787, at Straubing, in Bavaria. 
Being left an orphan when quite young, he was apprenticed 
to a glass manufacturer, who kept him hard at work all day. 
But he longed so much for knowledge that he borrowed 
some old books and spent his nights in learning. In the 
year 1801 the house in which he lived fell down one night 
and killed all the people in it except young Fraunhofer, 
and his cries being heard by the people outside, they set to 
work to try and release him. It happened that Maximilian 
Joseph, Elector of Bavaria, came to see the accident, and 
he encouraged the workmen so much, that in four hours the 
young man was dug out, wounded, but alive. The Elector 
was so much interested in this narrow escape, that he gave 
Fraunhofer eighteen ducats, and the lad used the money to 
buy himself off from his apprenticeship in order to have some 
free time for study. After this he lived by polishing lenses, 
and he worked so well that he soon became the master of 
a business, and was able to spend his spare time in the study 
of Physics and Astronomy, which he loved passionately. 
Finally he became manager of the physical laboratory of an 
academy in the town of Benedictbaiern, near Munich. 

Fraunhofer's Discoveries about the Spectrum, 1814 



CH. xxxiv. FRA UNHOFER'S DISCO VERIES. 335 

— From having been constantly at work as an optician, 
Fraunhofer had been led to study the subject of light, and 
among other experiments lie repeated those of Newton ; and 
it happened that he too used a narrow slit, as Wollaston 
had done. Thus he also noticed the black lines which 
divided the colours, and by making his slit very narrow and 
using prisms of very pure glass he discovered in a ray of 
sunlight no less than 576 of these black lines. Plate I., 
No. 2, gives a few of the principal of these, to which he put 
letters, and which have ever since been called ' Fraunhofer's 
lines.' As none of these lines appear when the light of a 
candle or lamp is passed through a prism, Fraunhofer con- 
cluded that sunlight must be defective, and some of its 
coloured rays must be missing. For, as numberless waves 
of coloured light are passing through the slit and the prism 
spreads them out so that each set of waves makes an 
upright image of the slit on the spectrum, if any waves were 
missing there would be a dark image of the slit instead of 
a coloured one. 

By far the best way of understanding this is to see it for 
yourself. Sir John Herschel says that a little inexpensive 
instrument may be easily made with a hollow tube of metal, 
blackened inside, a prism fixed in it, and a metal plate with 
a narrow slit fastened across the end of the tube, and Mr. 
Knobei tells me he has made one still more simply by 
placing a prism in a slit at one end of a cigar-box, and 
looking through another slit at the other end. With 
this several lines may be seen, but if even this is 
not to be had, you may gain some idea of the prin- 
ciple of the dark lines by the following illustration. 
Colour a strip of paper exactly like the continuous 
spectrum, No. 1, Plate L, and then cut it across into very 
narrow strips and place them in order side by side on 



336 NINETEENTH CENTURY. pt. hi. 

a dark ground ; each strip will represent an image of the 
slit, and the whole will be a continuous spectrum as before. 
But now suppose one set of waves to be wanting; take out 
one of your strips and you will have a dark space. This 
represents one of the black lines in the spectrum where a 
dark image of the slit is thrown, and if you take out those 
which correspond to the lines in the sun spectrum No. 2, 
you will have an illustration of ' Fraunhofer's lines.' 

Fraunhofer measured these black lines with the greatest 
care, and he found that in every ray of sunlight they came 
exactly in the same places. Then he tried the light of the 
moon and Venus ; still the black lines were the same, for 
these planets, as you know, only shine by the light of the 
sun. But, when he turned his telescope to the stars and 
caught their light, he found a difference. There were dark 
lines in the star-spectrum, but they were not all in the same 
place as those in the sun-spectrum, as you will see if you 
compare No. 2, Plate I., with the star-spectrum, No. 5, in 
which the lines seen on the right-hand side of the solar 
spectrum are entirely wanting. 

Fraunhofer, therefore, argued in this way : If the black 
spaces were caused by some of the waves being stopped in 
coming through our own atmosphere, they would be the same 
in any spectrum wherever the light came from. But as 
these dark spaces are different in the starlight from what 
they are in the sunlight, there must be some real difference 
between the light of the sun and the light of the stars before 
it comes to us. This was the first step in the study of the 
heavenly bodies by means of spectrum analysis. 

Experiments on the Spectra of different Flames, 
1822. — For more than forty-five years these black lines re- 
mained a complete puzzle to all who studied the spectrum, 
but in the meantime Sii John Herschel, Mr. Fox Talbot, 



ch. xxxiv. SPECTRA OF DIFFERENT FLAMES. 337 

Sir David Brewster, and others, had made many valuable 
experiments upon the colours produced by different burning 
lights. You know already that it is possible to make 
coloured flames by burning certain substances. For in- 
stance, if you put common salt in a spirit-flame, it will burn 
with a yellow colour, while a substance called nitrate of 
strontium will give a brilliant red flame, and is used in making 
red fire for the theatres. Many other metals and earths, 
however, tinge the flame so slightly that you cannot see the 
colour, and it is only by passing the light through a slit and 
examining it by means of a prism that you can detect it. 

Light from flames and from white-hot solids and liquids 
when passed through a prism produces a continuous spec- 
trum, that is, a coloured band unbroken by any dark lines. 
A lighted gas jet, a white-hot poker, or a flow of white-hot 
molten iron, will all give the continuous spectrum No. 1, 
Plate I. But gases or vapours, when heated so as to be- 
come luminous without burning, do not give a continuous 
band of colour, they only produce a few bright lines, such 
as those in Nos. 3 and 4. You can see this by putting a 
pinch of salt into a candle-flame, and examining it through 
a small spectroscope. The sodium in the salt will be 
reduced to a luminous vapour in the flame, and will give 
the bright line in No. 3 in the table of spectra, standing out 
from the continuous spectrum given by the candle-flame. 

Now there is a remarkable peculiarity about these bright 
lines formed by gases or vapours, namely, that they are 
different for the gas or vapour of every different substance. 
Thus, if you burn any substance containing sodium, a bright 
yellow stripe will appear as in No. 3 ; while hydrogen will 
give one red, one blue, and one violet stripe, as in No. 4. 
This test is so true and delicate that the hundred and 
eighty-millionth part of a grain of sodium will give the 



338 NINETEENTH CENTURY. ft. hi. 

yellow line ; nor does it matter if many incandescent gases 
are mingled together, for the vapour of each one will give its 
own lines without interfering with the others. 

It was Sir John Herschel in 1822 who first suggested that 
by reducing substances to incandescent gases in a flame, and 
marking the bright lines which they produced, it would be 
possible to detect the most minute quantities of any metal 
or earth which they contained, and Mr. Fox Talbot carried 
out this suggestion in 1834. By this means in the course 
of time, spectroscopists, or men who made the spectrum their 
study, were able to map out accurately the coloured lines of 
every known substance ; and what is still more wonderful, 
new metals were actually discovered by the new bright lines 
they threw on the spectrum. The first two of these new 
metals, called Ccesium and Rubidium, were discovered by 
Bunsen and KirchhorT in i860; the third, called Thallium, 
which throws a beautiful green line, was found by Mr. 
Crookes in 1861 ; the fourth, called Indium, which gives 
two indigo- coloured lines, was first seen by Bichter and Reich 
in 1864; and a fifth, called Gallium, was discovered by M. 
Lecoq de Boisbaudran in 1875. Thus spectrum analysis 
gives us an entirely new and sure way of analysing or dis- 
covering the different elements in any substance. 

Bunsen and KirchhofF explain the Dark Lines in 
the Sun Spectrum, 1861. — But for a long time no one 
could solve the question of the black lines in the solar spec- 
trum. Sir David Brewster came very near to it once, but 
just failed to hit upon the truth. 1 At last, in 1861, only 

1 Sir William Thomson states in his address to the British Associa- 
tion in 187 1, that Professor Stokes gave the true explanation of these 
lines in his lectures at Cambridge in 1851, although he did not publish 
anything about it, and his idea was not generally known. Balfour 
Stewart had also shown in 1858 that a body absorbs the same kind and 
amount of light and heat rays which it radiates when heated. 



CH. xxxiv. BUNS EN AND KIRCHHOFF. 339 

fourteen years ago, Bunsen and Kirchhoff, two celebrated 
professors of chemistry and physics at Heidelberg, discovered 
the secret. 

These two men had been making a long set of careful 
experiments upon all the different substances of our globe, 
burning them and examining their vapours one by one, 
and marking the bright lines of each upon the spectrum. 
In doing this they did not use one prism only as Fraun- 
hofer had done, but four (see Fig. 61), so arranged that 
the light coming in through a slit at the beginning of the 




Fig. 61. 
Kirchhoff s Spectroscope (Roscoe). 

tube a, was spread out more and more through each prism 
as it passed, and fell in a spectrum on the object glass, c, of 
the telescope b, through which they examined it. They 
soon found that in order to mark the exact position of the 
bright lines of each gas upon the spectrum, they wanted some 
fixed measure, and it occurred to them that the black lines 
of the solar spectrum, which never change, would make a 
good scale with which to compare all the others. So they 
arranged their spectroscope in such a manner that one-half 



34° NINETEENTH CENTURY. PT. in. 

of the slit was lighted by the sun and the other half by a 
luminous gas. In this way No. 2, Plate I., would appear 
above, and No. 3, for example, immediately below it. 

While doing this they could not help remarking that the 
bright yellow line of the sodium spectrum, No. 3, was exactly 
in the same position as the black line, d, in the solar spec- 
trum j 1 and KirchhofF found that when he passed a faint ray 
of sunlight through luminous sodium vapour (so as to make 
the two spectra, 2 and 3, cover each other), the yellow line 
exactly filled the black line with its light. He now wished 
to see how bright he could make the solar spectrum without 
overpowering the light of the sodium, so he let the full sun- 
shine pass through the sodium flame. To his great aston- 
ishment he saw the black line at d start out more strongly 
than ever. The sodium light while being overpowered itself 
had absorbed some of the yellow light of the sun ! 

This suggested to him the idea that the black line d must 
be caused by the white light from the sun passing through 
sodium vapour before it reaches us. There was a very simple 
way of proving whether this were so, for burning solids, you 
remember, give a continuous spectrum (1, Plate I.); there- 
fore, if he could produce a dark line by passing the light of 
a burning solid through glowing sodium vapour, he would 
imitate one of the defects in sunlight. So he burned a lime- 
light, and when he had the continuous coloured band in his 
spectroscope, he burned a flame coloured by sodium between 
the lime-light and the prism. The experiment was quite 
successful ; the dark space, d, started out upon the spectrum, 
and thus he proved beyond doubt that incandescent or glow- 
ing sodium vapour absorbs out of white light exactly those same 
rays which it gives out itself when glowing. 

1 This line is really formed of many lines which can be seen in a 
powerful spectroscope, but it appears single in a small instrument. 



ch. xxxiv. THE SOLAR SPECTRUM. 34 1 

He repeated the experiment with other burning metals, 
such as potassium and strontium, and always with the same 
result. Each mcandescent gas absorbed out oj white light 
exactly those rays which it gave oat itself when glowing. 

The black lines in the solar spectrum were now explained, 
for each one of them must imply that some particular ray of 
sunlight has been absorbed by a gas between the sun and 
us, and it must have been absorbed near the sun, as Fraun- 
hofer had pointed out, because the lines are different in 
light which comes from the stars, showing that in that case 
it has passed through other kinds of gases. Therefore 
KirchhorT concluded that round the solid or liquid body of 
the sun, which gives out white light, and would of itself pro- 
duce a continuous spectrum, there must be an atmosphere 
of gases of different kinds, which absorb or destroy particular 
rays of light, and prevent them reaching us. 

If this is the case, it is clear that we can tell from the 
lines in the spectrum what gases and vapours there are in 
this solar atmosphere. For example, there must be sodium 
which cuts off the rays which ought to come to d, and there 
must be also iron, magnesium, calcium, chromium, potas- 
sium, rubidium, nickel, barium, lead, copper, zinc, strontium, 
cadmium, cobalt, uranium, cerium, vanadium, palladium, 
aluminium, titanium, hydrogen, and carbon, for the bright 
lines of all these metals are wanting in the solar spectrum, 
showing that the white light from the body of the sun 
must have passed through their gases. Sir W. Herschel 
had supposed the sun to be a dark body surrounded by a 
luminous atmosphere. But we see that spectrum analysis 
shows just the opposite to be true. The body of the sun 
must be an intensely heated body giving out light, and if 
it is composed of gas it must be so dense as to act as a 
liquid and give a continuous spectrum. This body is called 
the photosphere^ or light-giving sphere; and around it lies the 



342 NINETEENTH CENTURY. PT. in. 

solar atmosphere in which the gases above mentioned have 
been discovered. This atmosphere is supposed to be from 
500 to 1000 miles high, and it has still another envelope 
outside it. In 1842 a white light or corona was seen round 
the sun when it was totally eclipsed by the moon, and red 
flames were observed shooting up into it. We do not 
even now know clearly what this corona is, but the red 
flames or 'prominences, 5 as they are called, were studied 
during the eclipse of 1868 by Professor Janssen in India, 
and Mr. Lockyer in England, and they both saw two vivid 
hydrogen lines (see No. 4, Plate II.), together with a third 
line not yet well understood. The red prominences then 
are made up chiefly of hydrogen gas, and Janssen and 
Lockyer proved that they are jets from an envelope of this 
gas which may be observed everywhere round the sun's 
atmosphere to a height of 5000 miles. To this envelope 
Mr. Lockyer has given the name of chromosphere, which 
has been generally adopted, and to him we owe a number 
of important conclusions as to the sun's atmosphere, and 
the nature of sun-spots and prominences, too lengthy to be 
given in this work. 

It is only the bright light from the body of the sun which 
prevents our seeing this hydrogen envelope at all times, and 
Lockyer and Janssen discovered independently of each 
other an ingenious way of making the hydrogen visible 
even in broad sunlight. They passed the light through 
many prisms at such angles that it was spread out till it 
became very faint indeed, and then it no longer hid 
the hydrogen lines, and they could be clearly seen. The 
'red prominences' or ejections of brilliant incandescent 
vapours from the chromosphere vary very much both 
in their height and the time they remain. Some shoot 
up 15,000 or 20,000 miles in a minute and fall back 



ch. xxxir. THE SOLAR SPECTRUM. 343 

like jets of water ; others remain for some days, and Respighi 
tells us that they reach a height of 80,000 miles or more. 
Thus we have evidence in the sun of a photosphere, or lumi- 
nous body, in the centre, an atmosphere of cooler gases round 
it which absorbs part of its light and causes the dark lines 
in the spectrum, and a chromosphere or coloured sphere of 
hydrogen gas which throws out jets of enormous height into 
a corona, the nature of which is as yet very imperfectly under- 
stood. The spots on the sun which Galileo noticed have also 
lately been much studied, especially by De la Rue, Balfour 
Stewart, and Loewy : they appear to be hollows which open 
from time to time in different places in the body or photo- 
sphere of the sun. We cannot discuss them here, but spec- 
trum analysis has helped to prove that they are depressions. 

The solar spectrum has now been mapped out with 
wonderful accuracy, and the name of Professor Angstrom, 
of Sweden, will always be remembered as one of the most 
able workers in this path. 

Dr. Huggins and Dr. Miller examine the Stars by 
Spectrum Analysis, 1862. — Only a few months after 
Kirchhoff had proved that the black lines in the solar spec- 
trum reveal to us what elements exist as gases around the 
sun, two English chemists, Dr. Miller, who died a few years 
ago, and Dr. Huggins, who is still living, began to try the 
same experiments with the other heavenly bodies. 

Their instruments were now much more perfect than 
those which Fraunhofer had used, and they were able to see 
the effects of our own atmosphere upon sunlight. When 
the sun is setting and its light has to pass through a long 
layer of air before it reaches us, faint lines appear on the 
spectrum, because some light is absorbed by the watery 
vapours in our atmosphere. Now, when Miller and Huggins 
examined the light which comes from Jupiter, they found 



344 NINETEENTH CENTURY. PT. ill. 

three or four lines like those caused by our atmosphere, 
showing that Jupiter must have an atmosphere partly, but 
not entirely like ours. Mars and Saturn also both showed 
these atmospheric lines, and so did Saturn's rings, proving 
that a similar atmosphere must spread over them also. But 
our moon gave none of them, and this agrees with other 
evidence in showing that the moon has no atmosphere. 

They next passed on to examine the light of the stars, 
and this was by no means an easy task, because the stars 
are so far off that their light is very faint and difficult to 
catch. Nevertheless they proved that round one star, called 
Aldebaran (No. 5, Plate I.), there must be an atmosphere 
of hydrogen, sodium, magnesium, calcium, iron, tellurium, 
antimony, bismuth, and mercury, and you will notice that 
the last four of these are not found in the sun. In the 
light of the star Betelgeux in the constellation Orion, and 
in another star, called P Pegasi, no hydrogen is found, but 
it is found in all the other stars that have been examined, 
together with many other substances. In some of the stars 
there are besides lines which must be produced by the 
vapours of substances different from any yet known upon 
our earth. 

Dr. Huggins proves that some Nebulae are Gaseous, 
1864. — And now we come to a very interesting experiment. 
You will remember that astronomers doubted Sir W. Her- 
schel when he suggested (p. 285) that some of the nebulae 
are not made of tiny stars, but of gas which is forming into 
stars. In 1864 Dr. Huggins began to examine these nebulae 
with the spectroscope, and he found that they did not give 
a band of colour with dark lines upon it as the stars do, 
but a few faint coloured lines on a dark ground, such as we 
know are produced by glowing gases and vapours. If you 
compare the spectrum of sodium (No. 3), or of hydrogen 



ch. xxxiv. SPECTRUM ANALYSIS, 345 



(No. 4), with the nebula spectrum (No. 6), you will see at 
once that the nebula spectrum is that of a luminous gas, 
and so the truth of Sir W. Herschel's idea was proved, and 
there can be now no doubt that the light of some of the 
nebulas comes from gaseous matter ; chiefly, so far as we 
can learn, of nitrogen and hydrogen. 

Spectra of Falling Stars and of Comets. — I have 
said that it was difficult to examine the spectrum of the 
stars and nebulas, but something which to an ordinary 
observer seems still more wonderful has been lately done. 
Mr. Alexander Herschel and others have actually caught 
the light of falling stars in the spectroscope, and in this 
way have discovered that some of them give a continuous 
spectrum, showing that they are incandescent solid bodies, 
while others give a gas spectrum, on which are the bright 
lines of potassium, sulphur, and phosphorus, and sodium. 
Even comets, those strange visitors to our solar system, 
have now had their light analysed. In 1864 Donati 
succeeded in obtaining the spectrum of a comet, and found 
that, besides the continuous coloured band produced by 
the sunlight reflected from its surface, there were three 
bright bands, yellow, green, and blue, separated by wide 
dark spaces. This showed that the comet was self-luminous 
and formed, at any rate partly, of glowing gas. In 1868 
Dr. Huggins discovered that in Winnecke's comet this gas 
gave the same spectrum as our 'marsh or olefiant 5 gas 
when it is made luminous by electricity in a vacuum tube, 
and since then this hydrocarbon spectrum has been found 
in all comets examined. The gases of sodium and iron 
have also been detected in the tails of comets which have 
passed very close to the sun, and were therefore probably 
in a great state of electrical excitement. Thus comets, 
though very complex in their nature, and so attenuated 



346 NINETEENTH CENTURY. pt. in. 

that it is very difficult to analyse their light, have been 
made to reveal their secrets. So far as is yet known, 
they are composed chiefly of gas made luminous by 
electrical disturbance, though some comets at least have 
probably a metallic core, similar to that of meteorites. 

Travelling Stars studied by the Spectroscope. — 
Nor has the spectroscope merely enabled the chemist to 
analyse the materials in distant suns, and ascertain their 
physical and chemical composition. It has also enabled 
them to measure movements otherwise inappreciable, and 
actually to calculate the rate at which some stars are 
travelling towards, and others away from, our earth. It 
is an old conjecture that a star has a red appearance when 
it is moving from the earth, or blue if it is moving towards 
it, but it has been shown that unless this movement is very 
great, the change of colour would not be perceptible to 
ordinary observation. The German physicist, Dopier, in 
1 84 1, was the first to point out that the rate of movement 
of a star might be measured by its change of colour, 
because this change depends upon the succession of light- 
waves upon the eye being more rapid when a star is 
approaching, and less rapid when it is receding. Such a 
change, however, can only be rendered perceptible by the 
spectroscope, and in this way Dr. Huggins measured the 
movement of Sirius or the dog-star. It must be remem- 
bered that the position of the lines which form the spectrum 
of any star depends upon the rapidity of the vibrations of 
the rays which produce them. Now, if a star be receding 
from us, it will send fewer vibrations in a second, conse- 
quently its colour will change, and its lines move towards 
the red end of the spectrum. It is necessary, therefore, 
first to identify some of the lines of a star-spectrum with 
the lines of some substance such as hydrogen or sodium, 



ch. xxxiv. CELESTIAL PHOTOGRAPHY. 347 

and then to observe how far the star lines differ from exact 
coincidence with the lines of the incandescent gas. Dr. 
Huggins established by this means the fact that Sirius is 
moving away from our earth at the rate of about 25 miles 
a second, after allowing for the motion of our own solar 
system through space. This method has now been applied 
to a large number of stars, not only by Huggins and others, 
but also on a large scale at the Greenwich Observatory. 

Celestial Photography. — rWhile all these wonderful 
results have been obtained by the spectroscope, photography 
has been advancing so rapidly that the very mountains and 
valleys in distant planets, and the impressions of the still 
more distant stars, and of fleeting comets, are now brought 
under our eyes in photographs. In 1864 Mr. Rutherford 
produced his magnificent photographs of the moon, and of 
star-groups, especially the Pleiades. In 1880 Professor 
Draper of America photographed the nebula of Orion. 
In 1885 the brothers Henry of Paris took photographs not 
only of the remotest planets, but even of the Satellites of 
Neptune and Saturn, the last of which is so faint that it 
can only be seen with the most powerful telescope. Nor 
is this all, for they actually discovered by photography a 
nebula surrounding the star Maia of the Pleiades, which 
till then was quite unknown. Encouraged by such great 
success, astronomers now propose to photograph the whole 
of the heavens; and on April 18, 1887, a memorable 
International Congress took place in Paris, at which it was 
agreed to carry on the work at selected stations all over the 
world. Not only in Europe, the United States, and 
Australia, but in Mexico, Brazil, Chili, the Argentine 
republic, and numerous other countries, preparations are 
being made, and when the work is completed it is estimated 
that there will be 11,000 plates covering 2000 square 



348 NINETEENTH CENTURY. pt. hi. 

feet in all, and representing photographs of between ten 
and twenty million of stars. With such a result as this we 
may well close our short sketch of the work which light 
has done and is doing for astronomy. They were results 
little dreamed of when Davy proposed to take sun-pictures, 
and Fraunhofer measured the dark lines in the spectrum, 
and they have been obtained step by step through honest 
patient work both in the improvement of instruments and 
in daily and hourly accurate observation and experiment. 



Chief Works consulted. — Roscoe's ' Spectrum Analysis ; ' ' Edin- 
burgh Review,' vol. cxvi. ; 'Philosophical Magazine,' i860 ; Proctor, 
' The Sun ; ' Tyndall's ' Lectures on Light ; ' ' Half-hours with Modern 
Scientists ; ' KirchhofFs ' Researches on the Solar Spectrum,' 1862 ; 
'Encyclopaedia Britannica,' art. 'Optics;' Ganot's 'Physics;' Wol- 
laston, 'On Dispersion' — ' Phil. Trans.' 1802; Lockyer, 'The Spec- 
troscope;' Miss Clerke, 'Astronomy of the Nineteenth Century;' 
Common, ' Astronomical Photography,' Nineteenth Century, Feb. 1887. 



en. xxxv. THEORIES OF HE A T. 



349 



CHAPTER XXXV. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Early Theories about Heat — Count Rumford's Experiments — Davy's 
Experiments — Mayer — Dr. Joule on Mechanical Equivalent of Heat 
— Indestructibility of Force, and Conservation of Energy — Dissipa- 
tion of Energy — Molecular Theory of Gases — Free Molecules in 
Vacuum Tubes. 

Early Theories about Heat. — From Light we will now 
pass on to Heat, and in this chapter I hope to show you how 
the philosophers of this century have discovered what heat 
is. The subject in itself is so vast that a mere sketch of all 
the men who have worked at it and their chief experiments 
would fill a volume of this size, and you must clearly under- 
stand that we can only select those examples which will best 
enable you to comprehend the nature of heat, and how it 
has been determined. 

Have you ever asked yourself what heat is, or why the 
mercury in a thermometer rises when it is put into hot 
water? The old philosophers considered heat to be a fluid, 
which passed out of substances when they were too full of 
it, and which, entering the mercury of the thermometer, 
swelled it out and made it rise. This was the general idea 
about heat up to the end of the eighteenth century, although 
Lord Bacon, more than two hundred years before, had 
suggested that it was not a fluid but a movement, and the 
philosopher Locke, in the seventeenth century, and Laplace 
in 1780, gave the same explanation. 



350 NINETEENTH CENTURY. pt. hi. 

Still most scientific men looked upon heat as a fluid, 
which they called caloric, until, in the year 1798, Count 
Rumford first showed by experiment that it is probably a 
kind of motion. In following strict chronological order, this 
discovery ought to have been mentioned at the end of the 
eighteenth century, but it belongs so intimately to the 
modern theory that it comes more naturally in this place. 

Count Rumford shows that Heat can be produced 
by Friction, 1798. — Benjamin Thompson, afterwards Count 
Rumford, was born in America in 1753. He spent his 
early life fighting in the English army against the Americans, 
in the War of Independence, and afterwards settled at 
Munich, and became aide-de-camp to the Elector of Bavaria. 
In 1798 he came over to England, where he was one of the 
founders of our Royal Institution, and finally he died in 
Paris in 1844. 

Rumford's inquiries into the nature of heat began in 
rather a curious way. He was very anxious to make the 
poorer people in Bavaria happier and more prosperous, and 
to accomplish this he persuaded the Elector of Bavaria in 
1790, to forbid any one to beg in the streets. Those who 
could not find work for themselves were taken up and kept 
in a kind of workhouse, where they were given good food 
and clothing, but were forced to work to pay for their own 
support. When this law was first passed, there were no 
less than 2500 beggars to be provided for, and Rumford was 
obliged to calculate very closely how he could find food and 
clothing, heat and light, for the least money. Accordingly 
he studied how fireplaces could best be built to prevent 
coal being wasted, and invented a lamp which gave a 
brilliant light, without burning so much oil as other lamps 
did. He even went so far as to make a complete set of 
experiments on different clothing materials, in order to see 



ch. xxxv. HEAT PRODUCED BY FRICTION. 351 

which kept in the most heat. It was in this way, and espe- 
cially in using steam for warming and cooking, that he first 
began to study the properties of heat, and he became much 
interested in the different ways in which it may be produced. 

It happened one day, when he was boring a cannon in 
one of the military workshops of Munich, that he noticed 
with surprise the great heat produced by the grinding of the 
borer against the gun. You can easily make a similar ex- 
periment by boring a hole quickly with a gimlet in a piece 
of hard wood, and on withdrawing the gimlet you will find 
that it is hot enough to burn your hand. Rumford examined 
carefully the gun and the chips which fell from it, and found 
that they were both hotter than boiling water. 

This led him to consider how it could possibly happen, 
if heat were a fluid, that the mere rubbing of two metals to- 
gether should produce it ; and he tried many experiments to 
find out whether the gun, the chips, or the borer had lost 
anything in consequence of having given out heat. But he 
could not discover that they were changed in any way; and 
moreover, he found that by going on boring he could make 
them give out heat as long as he liked, whereas if he had 
been drawing a fluid out of the metals it seemed to him 
that it ought to come to an end sooner or later. Then he 
considered whether the heat could come out of the air, and 
to avoid this he repeated the experiment under water, but 
still the metals grew hot, and even made the water warm, so 
it was clear they had not drawn any heat from that fluid. 

He now began to suspect that Bacon and Locke might 
be right, and that the rubbing together of the two metals 
might set their particles vibrating in some peculiar way so as 
to cause what we call heat. If this were so, then by great 
friction he ought to be able to produce any amount of heat, 
and to prove this he tried the following experiment. 



352 NINETEENTH CENTURY. pt. hi. 

He took a large piece of solid brass the shape of a can- 
non, and partly scooped out at one end. Into this he fitted 
a blunt steel borer, which pressed down upon the brass with 
a weight of ten thousand pounds. Then he plunged the 
whole into a box holding about a gallon of water, into which 
he put a thermometer, and fastening two horses by proper 
machinery to the brass cylinder he made them turn it round 
and round thirty-two times in a minute, so that the borer 
worked its way vigorously into the brass. Now notice what 
happened : When he began the water was at 6o° F., but it 
soon grew warm with the heat caused by the friction of the 
borer against the brass. In one hour it had risen 47 degrees 
up to 107 Fahr.; in two hours it was at 17 8°, and at the end 
of two hours and a half it actually boiled. 

1 It would be difficult,' writes Rumford, ' to describe the 
surprise and astonishment of the bystanders on seeing so 
large a quantity of water heated and actually made to boil 
without any fire,' and he adds that he himself was as de- 
lighted as a child at the success of the experiment ; and we 
can scarcely wonder, for he had proved the grand fact that 
heat is not a substance but a peculiar kind of motion. 

Rumford afterwards calculated that the friction caused 
by one horse pulling round the cylinder against the borer 
was sufficient to raise 26 lbs. of ice-cold water up to the 
boiling point in two hours and a half, thus showing that the 
heat obtained has a definite relation to the energy expended 
by the horse. 

Davy makes Two Pieces of Ice melt by Friction in 
a Vacuum, 1799. — Only a few months after Rumford had 
made the discovery that heat can be produced by friction, 
Sir Humphry Davy, whose history as a chemist you will read 
in Chapter XXXVII., proved the same thing by a different 
experiment. He took two pieces of ice, and by rubbing 



CH. xxxv. HEAT A VIBRATION. 353 

them together made them melt without any warmth being 
brought near them. In this case, as he said, no one could 
think that the heat came out of the ice, for ice holds less 
heat than water ; and in order to be quite sure that it did 
not come out of the air, he made a second experiment. He 
took a small piece of ice and put it in a machine under an 
air-pump, by means of which he drew out all the air ; then 
he set his machine to work so that it rubbed against the ice, 
and in this way he melted the whole lump, without any air 
being present. 

Heat a Vibration. — From these experiments Davy came 
to the conclusion 'that heat is a peculiar motion, probably a 
vibration of the corpuscles (that is the little particles) of 
bodies, tending to separate them.' Thus for example, when 
you put a saucepan full of water on the fire, the quivering 
motion which is going on in coals as they burn passes into 
the iron of the saucepan, and through it to the water. Im- 
mediately all the little particles of which the water is com- 
posed are pushed asunder as if they were trying to get away 
from each other ; but as they are still held together by the 
force of attraction, they vibrate to and fro, struggling more 
and more to get free, and it is this motion which causes in 
us the feeling of heat when we come in contact with it. 
Then, if a thermometer be placed in the water, the vibration 
passes on through the glass of the tube into the mercury, and 
the particles of mercury are also set in motion, and so the 
mercury swells and rises in the tube. 

The Cause of Latent Heat explained. — And now, if 
you will look back for a moment to Chapter XXVIII., and 
read again about the ' latent heat ' which puzzled Dr. Black 
so much, you will see how beautifully it can be explained 
by this theory that heat is a kind of motion. You will 
remember that, however much heat he put under a piece 



354 NINETEENTH CENTURY. PT. ill. 

of ice he found that the temperature of the water would 
not increase above o° Cent, so long as a morsel of ice 
remained unmelted ; and again, that boiling water never 
grew hotter than ioo° Cent., while it was being turned into 
steam. Now if we look upon heat as a vibration, we can 
understand that the motion which is sent into ice from the 
fire below will all be employed in overcoming the force of 
attraction and separating the particles of ice so as to turn 
the solid into a fluid, and it will only be when the last 
particles are free that there will be any movement to spare 
so as to produce the quivering motion of heat. Then if 
you go on heating the water still more, the struggling move- 
ment will continue between the force of attraction and the 
force of motion, and so the water will grow hotter and hotter, 
till at last at ioo° Cent, the force of motion wins the battle, 
and the tittle particles fly asunder and float away as steam ; 
and from that moment all the extra movement is employed 
in forcing asunder particle from particle, till all the water 
has passed away in vapour. 

It was for this reason that Watt had to use so much 
more cold water to cool down steam of ioo° Cent, than 
to cool down water of ioo° Cent; for in cooling down 
steam he had not only to get rid of the quivering motion 
of heat, but of all the extra force which was holding the 
particles asunder. 

Dr. Joule's Experiments on the Mechanical Equiva- 
lent of Heat, 1849. — It had now been shown that energy 
could be converted into heat. In Rumford's experiment the 
energy had been derived from the horse, and in Davy's case 
from himself, as he rubbed the pieces of ice or worked the 
machine. But neither of these experiments measured 
accurately the amount of energy which produced a given 
quantity of heat. Rumford had, indeed, made a rough 



ch. xxxv. MECHANICAL EQUIVALENT OF HEAT. 355 

calculation ; but when a horse walks round and round, we 
cannot measure how much strength he gives out, and in 
order to prove that energy by itself can produce heat we 
must measure exactly how much work produces a definite 
increase of temperature, — say of i° Fahr. — and then see if 
that amount of heat can be turned back again into work. 
This was done by Dr. Joule, of Manchester, a celebrated 
physicist, who is still living. 

In 1839 a Frenchman named M. Seguin, and in 1842 
a German physician, Dr. Mayer, of Heilbronn, both sug- 
gested that by careful experiments it might be found out how 
much work must be done to produce a certain increase of 
temperature, and Dr. Mayer made many calculations about it. 
In 1 843, without having heard of Dr. Mayer's suggestion, Dr. 
Joule, who had previously discovered in 1840 the law cf 
heat evolved by Voltaic electricity, began those famous ex- 
periments which have formed the foundation of the dynami- 
cal theory of heat, or the theory of heat produced by mechanical 
energy, and he completed them in 1849. A description of 
one of his experiments will explain the results he obtained. 
He took a weight, a, Fig. 62, p. 349, which weighed ilb. and 
fastened it by strings to the roller,// On to the wheel, b, 
of this roller he wound another string which passed round 
the roller r, and this roller was attached to a paddle which 
was shut into the box of water, c. He next wound up the 
string on the roller / so as to draw up the weight a, and 
then set it free. Immediately the force of gravity drew the 
weight down to the ground, and in doing so pulled round 
the wheel b, and consequently the roller which turned the 
paddle in the water. When the weight reached the ground 
he took out the little pin, p, which fastened the paddle to 
the roller, so that he could wind up his apparatus without 
disturbing the water and begin again. 

17 



35^ NINETEENTH CENTURY. pt. hi. 

Now observe how this measured the work done and the 
heat produced. Every time the weight fell, it turned the 
paddle, and so, by agitating the water, added to its heat. 
The scale, d, told him exactly how far the weight fell, while 
the thermometer, /, in the box told him how much hotter 
the water grew. At the end of an hour, therefore, he had 
only to see how many feet his pound-weight had fallen, and 
how many degrees of Fahr. the temperature of his water had 
risen ; and after allowing for the friction of his machinery 
and for the heat lost in the cooling of his vessel, both of 
which he ascertained by careful experiments, he could tell 
how much energy had been expended in producing the 
rise of temperature. In this way he found that a weight of 
i lb. would have to fall 772 feet in order to raise the tem- 
perature of 1 lb. of water by i° Fahr. 

He next tried the same experiment with oil and with mer- 
cury instead of water, and also measured the heat produced 
by rubbing together two plates of iron ; and in every case he 
found that a certain amount of work gave a certain amount 
of heat and no more. For example, if the weight in Fig. 
62 fell double the distance, the temperature of the water was 
raised two degrees instead of one, while if it fell only half the 
distance, or 386 feet, the water was only raised half a degree. 

In this way Dr. Joule established what is called the 
mechanical equivalent of heat, namely that the fall of a pound 
weight through 772 feet sets free enough mechanical energy 
to raise the temperature of a pound of water i° Fahr. And 
now you must try to form a clear idea what this means. 
Looking at the diagram, try to picture to yourself whaf 
would be taking place if the weight were able to fall the 
whole 772 feet without stopping. First, a man must wind 
up the weight, and in doing this he uses working power or 
energy to overcome the force of gravitation which is pulling 



ch. xxxv. DYNAMICAL THEORY OF HEAT. 



357 



the weight down to the earth ; so that the machine starts 
with a certain stock of energy stored up in the weight, and its 
amount is called 772 foot-pounds because it has raised a 
weight of 1 lb. to a height of 772 feet. This stock of 
working-power philosophers call potential e?iergy, or possible 
energy which may be called into use at any time. When 
the man sets the weight free, it begins to fall, drawn down 
by the force of gravity, and the stock of energy is set free. 
What becomes of it ? It passes by the wheel b into the 
roller r, and, turning the paddle in the box enters the water. 




Fig. 62. 
Joule's Experiment on the Conversion of Motion into Heat (Phil. Trans.) 

a, Weight. B, Wheel of the roller, ff c, Vessel containing water and the paddle. 
D, Scale to measure the distance that the weight falls, e, Paddle contained in 
the vessel, c. ff, Roller turned by the falling weight, r, Roller turning the 
paddle, p, Pin which joins the roller and the paddle, t, Thermometer plunged 
in the vessel, c. 

If the water were free, the motion would pass on into the air 
and we should lose sight of it ; but the water is shut in and 
the energy cannot escape, so now it employs itself in dashing 
to and fro all the little particles which make up the water, 
and producing the effect we will call heat. Thus the 



358 NINETEENTH CENTURY. ft. iil 

mechanical energy of the weight, derived from the man who 
wound it up, is expended in fluid friction in the box and 
thus converted into heat. 

Hirn's Experiments on Heat converted into 
Mechanical Energy. — If you have understood this ex- 
planation, you will have some idea of the theory that 
mechanical energy may be converted into heat: but to 
complete the proof we require not only to turn work into 
heat, but also to turn heat into work. This had already 
been done many years before by a French engineer, M. 
Carnot, though he did not understand its real significance, 
but it has now been most beautifully proved by a long 
series of experiments made by M. Hirn, of Colmar, in 
Alsace. It was already known exactly how much heat 
could be obtained from every ton of coal consumed. What 
M. Hirn did was to find out how much of that heat was 
converted into useful work in an engine. This was by no 
means a simple task, for much heat is lost in various ways 
in passing through the engine ; and even when he thought 
he had allowed for all this, it was found that some of the steam 
had turned back into water on its way, and thus used up 
some of the heat. At last, however, when all was carefully 
measured and calculated, he found that if it had been 
possible to turn all the heat passing through the engine into 
work, then for every i° Fahr. added to the temperature of a 
pound of water, enough work would have been done to raise a 
weight of i lb. to a height of 772 feet. 

Conservation of Energy. — And thus we arrive at one 
of the grandest discoveries of modern science, namely, that 
the whole amount of energy, or power of doing work, pos- 
sessed by any set of bodies, remains unaltered whatever 
transformations it may undergo. It may exist in one of 
two forms — either as potential or stored-up energy, which is 



ch. xxxv. CONVERSION OF MOTION INTO HEAT. 359 

unseen by us, or as visible energy, when it is actually per- 
forming work ; but while it changes from one form to another 
its amount never alters. Thus in Joule's experiment the 
energy stored up in the 1 lb. weight which had been pulled 
up 7 7 2 feet was gradually transformed, as soon as the weight 
was released, into an amount of heat capable of raising the 
temperature of a pound of water i° Fahr. ; while Hirn 
showed, on the other hand, that exactly this amount of heat 
would, if it could be turned back again into energy, raise the 
1 lb. weight to the height of 772 feet at which it stood 
before. 

The potential energy, or power of doing work, remained, 
therefore, exactly the same whether it was stored up in the 
weight or in the hot water. And even though we know 
that practically some energy disappears at every part of a 
machine when it is at work, yet this is not lost ; for it turns 
into heat, or some other form of energy, wherever it disap- 
pears as motion. If you grease the wheels of a machine, 
you will detect this heat beginning to do work again by 
turning the solid grease into a liquid. 

By whatever means, therefore, heat is turned into work, 
or work into heat, the energy which causes them both 
remains the same, and this is one out of many proofs that 
energy cannot be destroyed, but is only lost in one form to 
reappear in another. 

Although the experiments and calculations which have 
proved heat to be a mode of motion are some of the most 
interesting which have been made of late years, yet they are 
by no means the only ones. In 181 1 Sir John Leslie 
carried on a most interesting series of observations on the 
reflection of heat : and the Italian physicist Melloni has 
traced the whole passage of heat-rays through different 
solid bodies. All these discoveries are clearly and simply 



360 NINETEENTH CENTURY. FT. in. 

described in Professor Tyndall's work on ' Heat,' where you 
may also find the great additions that he has himself made 
to the work of these men. 

We must content ourselves here with remembering that 
the physicists of the nineteenth century have shown that 
heat is 'a mode of motion,' and have traced it through 
all its many wanderings both in earth, air, and sky. They 
have even followed it from the sun down to our earth, 
through the plant-world into the beds of coal which are 
stored up in our rocks, and back again, when this coal is 
burnt, to the motion which carries our steam-engines and 
steam-ships across the world. The great German physicist 
Helmholtz, to whom we owe the greatest modern essay on 
the conservation of energy, states that ' a pound of the 
purest coal gives, when burnt, sufficient heat to raise the 
temperature of 8086 pounds of water i° Cent. ;' and from 
this he calculates 'that the chemical force of attraction 
between the particles of coal and the quantity of oxygen that 
corresponds to it is capable of lifting a weight of 100 pounds 
to the height of twenty miles.' This chemical force was stored 
up in the vegetables of the coal when they obtained it from 
the sun's heat ages and ages ago, and now man sets it free 
to perform the work. * We cannot create mechanical force,' 
writes Helmholtz, 'but we may help ourselves from the 
storehouse of nature. The brook, the wind, which drive 
our mills, the forest, the coal-bed, which supply our steam- 
engines and warm our rooms, are the bearers to us of the 
small portion of the great natural supply which we draw 
upon for our purposes.' 

Dissipation of Energy— Sir William Thomson. — But 
the question still remains whether this natural supply will 
always be in such a condition as to perform actual work; 
and upon this point our great mathematician, Sir William 



CH. xxxv. CONSERVATION OF ENERGY. 361 

Thomson, has come to a conclusion which we must try to 
understand, however imperfectly. 

We have already seen when speaking of Hirn's engine 
that it is impossible to convert all the heat passing through 
the engine into work. Now, that portion which escapes in 
the form of heat, although it represents quite as much 
mechanical energy as it did before, is no longer useful in the 
same way, because it has become spread out or diffused ; and 
this happens whenever energy changes its form, whether 
from mechanical energy into electrical energy, from heat 
into work, from work into heat, or in any other way. In- 
variably a certain amount of energy is dissipated, or spread 
out in the form of diffused heat. 

The same amount of energy remains, it is true, but it is 
so uniformly distributed as to be no longer available for 
work ; for heat can only be turned into work when it passes 
from a hotter to a colder body ; therefore heat spread equally 
over all bodies in nature is lost as a working power, even 
though it represents the same amount of energy, which could 
be made to do work if it could be collected again into a 
condensed form. 

This fact of the dissipation of energy was first announced 
by Sir William Thomson in 1852, and he pointed out that 
it tends to let down, as it were, the working power of nature. 
We keep up our store by deriving fresh heat from the sun, 
and storing it up in the vegetable world, in wood, and coal, 
and also in the falling power of water which has been drawn 
up to the clouds by the sun's heat. But the sun's heat itself, 
and every operation going on in the universe, is caused by the 
transformation of energy, therefore dissipation must also go on 
with it ; and, unless there is some compensating power, the 
whole universe must be drifting very slowly into a state of 
rest. 



362 NINETEENTH CENTURY. pt. ni. 

But here we must remember that we are travelling 
beyond our knowledge. In spite of the great discoveries 
made in this century as to the nature of the sun, we are still 
in doubt as to the source from which this heat is derived ; 
still less have we any idea what is the source of that energy 
by which the heavenly bodies were first set in motion. We 
speak glibly of the universe, but our most powerful instru- 
ments, by revealing at every step in advance that more 
remains beyond, only open before us an ever-widening 
prospect, to which we cannot even conceive a limit. 

Molecular Theory of G-ases.— We stand on more solid 
ground when we investigate the energy exerted in our own 
planet, yet even here mathematicians and physicists have 
advanced so rapidly that their conclusions are almost beyond 
our grasp. Familiar as are the names of Graham and 
Andrews, Faraday and Tyndall, Helmholtz, Clerk-Maxwell, 
and Sir W. Thomson, yet the structure of matter, the 
theories of heat, electro-magnetism, and thermo-electricity, 
and similar subjects in which their grandest work has been 
accomplished, are only to be thoroughly understood by 
scientific men. 

Perhaps the best way of giving some notion of their in- 
vestigations is to state roughly — firstly, that they have followed 
energy, or the power of doing work, into its most hidden 
forms, detecting its action among the particles of a gas, 
measuring it in the electric current, and showing how it may 
be lost to us by dissipation (see p. 361), even though it is in 
itself indestructible ; and secondly, that they have succeeded 
in measuring not only the movements, but even the size of 
the smallest existing portions of matter, and have come 
very near to telling us even the nature of the atoms of which 
matter is composed. 

The celebrated Swiss mathematician Daniel Bernoulli, in 



ch. xxxv. MOLECULAR THEORY OF GASES. 363 

the seventeenth century, was the first to suggest that gases 
are formed of free particles or molecules in constant motion, 
and that the pressure of a gas upon the sides of the vessel 
containing it, is caused by the agitation of molecules within. 
Thus, for example, an ordinary air-ball, if held near the fire, 
expands, because the molecules of the air within move with 
more energy and beat with more force against the sides of 
the bag containing them. 

In our time Graham, Joule and Andrews, Clausius, 
Clerk -Maxwell and Boltzmann, Helmholtz and Sir W. 
Thomson, have enabled us to see these molecules with our 
imagination, dashing to and fro, hitting one against the other, 
and flying off in different directions and at different rates. 
They have ascertained, for example, that in hydrogen gas, at 
the ordinary temperature and pressure of our atmosphere, 
each molecule of hydrogen is moving at the rate of about 
6225 feet in a second, yet it must perform all its motions 
in an incredibly small space, for it is constantly striking 
against some other molecule, so that in that second of time it 
rebounds more than seventeen thousand million times. This 
number of collisions of the molecules will always correspond 
to the same temperature and pressure of the gas. But if 
more energy be imparted to the molecules the temperature 
will rise, for the more quickly they dash to and fro and 
strike each other the higher the temperature will be. When 
we heat a gas we are in fact increasing the energy of the 
molecules and making them dash to and fro more rapidly. 
This rebounding of the molecules is the reason, as Clausius 
showed, why, when two gases are brought together, it takes 
them some time to mix thoroughly, the new molecules have 
to fight their way among those which are already in the 
field. Dr. Graham had long before shown experimentally 
that the rate of diffusion is inversely as the square roots of 



364 NINETEENTH CENTURY. FT. III. 

the densities of the gases, and we now know that the vibra- 
tion of the molecules themselves is in this ratio. The 
collisions also explain, as Clerk -Maxwell has shown, why 
heat is conducted so slowly from one part to another of a 
gas. The molecules which we make more energetic by heat 
at one point hit against others and communicate their 
energy, and these again to others, till they all move at 
equal rates and the gas has an even temperature throughout. 
And now, perhaps, we might think that, having arrived 
at these infinitesimal movements among the molecules of 
matter, we had gone as far as human power could penetrate. 
But it is not so : Loschmidt in 1865, Stoney in 1868, and 
Sir W. Thomson in 1870, were able, in following out the 
discoveries of Clausius and Maxwell, to measure actually the 
size of the molecule itself. They tell us that two million 
molecules of hydrogen placed in a row would measure one 
millimetre, so that about 50 million would lie side by side 
in an inch. Nor is this all, for the spectroscope has revealed 
that even these minute particles are not mere rigid atoms. 
We have seen (p. 337) that a gas gives a spectrum of bright 
lines ; now these lines are caused by the vibration of the 
parts of the molecule itself, in consequence of its having been 
shaken by coming into collision with another molecule. Thus 
we have to picture to ourselves these molecules not only 
dashing to and fro and hitting each other, but each one of 
them during its passage between one concussion and another, 
quivering with the shocks it receives, and so giving out waves 
of coloured light, just as a bell when hit gives out waves of 
sound. The study of these vibrations and of the nature of 
the atoms of which these molecules are composed, forms 
some of the grandest work accomplished by Helmholtz and 
Sir W. Thomson, while the theory of electro -magnetism 
worked out by the late Professor Clerk-Maxwell rests upon 



ch. xxxv. FREE MOLECULES IN VACUUM TUBES. 365 

a series of vortices in and between these molecules, and is 
the best solution at which mathematicians have yet arrived 
on the subject 

Passage of Free Molecules in Vacuum Tubes.— 
Meanwhile Mr. Crookes was able in 1 8 7 7 to show by actual 
experiment the movement of the molecules of a gas in so- 
called 'vacuum tubes.' It is well known that even in the 
most perfect vacuum which we can obtain in a glass tube, 
an enormous number of molecules of gas or air always 
remain, and it is in consequence of the movements of these 
molecules under the influence of light or heat that a kind of 
windmill can be made to turn inside those curious glass 
bulbs, called by Mr. Crookes 'radiometers.' He has now 
shown that in very high vacua — about the millionth of an 
atmosphere — in consequence of there being comparatively 
few molecules in the bulb, their mean free path is long 
enough to enable them to travel across without materially 
interfering with each other. In this free state most curious 
effects are produced by currents of electricity. The mole- 
cules driven from the negative pole hit with such force 
against the glass that they make it glow with phosphor- 
escence, and substances such as the diamond and the ruby, 
which are scarcely phosphorescent under ordinary circum- 
stances, if placed in the path of these molecules, shine with 
extraordinary brilliancy. But the point of most importance 
is that the gas at this high exhaustion behaves quite differ- 
ently from ordinary gases, owing probably to the greater 
freedom of molecular action, and Mr. Crookes believes that 
it will be found to form a fourth state of matter, as distinct 
from the gaseous as the gaseous is from the liquid state. 

It may perhaps seem strange that, while speaking of 
these discoveries of theoretical interest in physics, we omit 
the description of the numerous inventions which have been 



$66 NINETEENTH CENTURY. pt. iil 

crowding upon us in the last few years, such as the phono- 
graph, the microphone, and the electric light, but it must 
be remembered that these are not strictly new discoveries 
in science, but applications of principles already discovered. 
Though of surpassing interest, they must be studied in 
detailed works, or find their place in a history of inventions. 
The last fifty years have been essentially a period of the 
application of scientific knowledge to practical life, and if 
any justification were needed of the study of pure science, 
it may easily be found in the fact that our railways, our 
telegraphs, our steamships, our manufactures, which have 
done so much for the prosperity of England, are all the 
results of scientific principles studied at first for their own 
sake, and many of them apparently as far removed from the 
affairs of daily life as the molecular theory of gases or the 
ultra-gaseous state of matter. 



Chief Works consulted. — Rumford's 'Essays,' vol. ii. — 'Friction a 
Source of Heat,' 1798; Davy's 'Works,' vol. ii. — 'Essay on Heat 
and Light ; ' Joule's ' Mechanical Equivalent of Heat ' — ' Phil. Trans.,' 
1850; Mayer's 'Forces of Inorganic Nature' — 'Phil. Mag.,' 1843: 
Tyndall's 'Heat a Mode of Motion;' Watts's 'Diet, of Chemistry,' 
art. * Heat ; ' Clerk - Maxwell's ' Theory of Heat ; ' Encyclopaedia 
Britannica,' 9th ed. art. 'Atoms;' Tait's 'Recent Advances in Physical 
Science.' 



CH. xxxvi. ELECTRO-MAGNETISM. 367 



CHAPTER XXXVI. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Electro-magnetism — Oersted — Ampere — Arago — Faraday — Thermo- 
electricity — Seebeck — Schwabe — Spots on the Sun — Sabine — 
Sun-spots and Magnetic Currents — Electric Telegraph — Wheat- 
stone — Cooke — Steinheil — Morse — Bain. 

Oersted discovers the Effect of Electricity upon a 
Magnet, 1829. — We left the history of electricity at p. 
262, at the point where Volta had shown in 1800 that two 
different metals joined by a wire and placed in acid and 
water will set up a current of electricity flowing from the 
one metal to the other, and back through a connecting 
wire. Every galvanic battery, that is, an apparatus for 
producing electricity by chemical action, is made on 
this principle. You will hear of Grove's battery, Bun- 
sen's battery, Daniell's battery, and many others, all of 
which have been invented in the present century ; but all 
these are only different and more perfect methods of carry- 
ing out Volta's discovery. The next great step in the study 
of electricity was made by Oersted, Professor of Physics at 
Copenhagen, in 1820, twenty years after the invention of 
the voltaic pile. 

Hans Christian Oersted- was born in 1777, and died in 
185 1 ; he was a very eminent man, and wrote many works 
in Latin upon chemistry and magnetism, but the one dis- 
covery which has made him famous was that of electro- 



( 



3^8 NINETEENTH CENTURY. pt. hi. 

magnetism. We have seen (p. 53) that the invention of 
the mariner's compass in the fifteenth century arose from 
Flavio Gioja noting that a needle which has been rubbed 
along a piece of loadstone always points north and south. 
But why should the needle lie in this direction? What 
force makes it turn round when you leave it free after 
placing it another way ? Ever since the fifteenth century 
people had asked this question, and when Volta and 
Franklin showed that electrical currents are constantly 
passing to and fro in our atmosphere, scientific men began 
to consider whether it might not be some force like elec- 
tricity which acted upon the magnet ; especially as it had 
been observed that when a ship was struck by lightning, 
the needle of the mariner's compass was sometimes thrown 
quite out of its right position. 

Still nothing was really known until the year 1 8 1 9. In 
that year, when Professor Oersted was one day making some 
galvanic experiments at a lecture, it happened that a magnetic 
needle poised upon a point (as in Fig. 63) was standing 
near the wire along which an electric current was passing. 
All at once, when the current was very strong, the needle 
became excited and began to turn round upon the point 
Oersted and his assistants were much surprised at this, and 
the consequence was that during several months Oersted 
made a series of experiments by which he proved that an 
electric current passing near a magnetic needle will always 
make It turn round so as to lie across the path of the 
current 

For example, if the bar of copper wire a &, supported on 
the glass rods e, e, be so placed that the end b points to the 
north and a to the south, then the magnetic needle c will He 
exactly in a line with the bar, because a magnet always 
points north and south. But if the two ends of the copper 



CH. XXXVI. 



ELECTRO-MA GNETISM. 



369 



rod a, b, are fixed to the wires of a voltaic battery d, Fig. 63, 
so that an electric current runs along the rod from a to b, 
then the north end of the needle will begin to move away 
from the north towards the west, that is towards the left side 
of the current ; and it will turn more and more as the cur- 
rent grows stronger, till it lies right across it, pointing direct 
east and west. 

This was a very grand fact, and it has become the begin- 
ning of a new science called electro-magnetism, for it shows 
that electricity and magnetism are connected in some 




Fig. 63. 
Magnet turned by an Electric Current. 

a 5, Rod of copper wire, c, Magnetic needle, d, Voltaic pile (explained p. 261). 
e e, Glass supports to prevent the current running down to the ground. 

peculiar way. Oersted did not publish an account of his 
experiments until 1820, and then the whole of Europe rang 
with the news of the discovery. 

Ampere, 1775-1864. — One of the first men who heard 
of it was Ampere, one of the professors at the Ecole Polytech- 
nique in Paris. We must pause a moment to learn something 
of the early history of this man, for it is very interesting. 
Andre Ampere was born at Lyons in 1775. When he was 
quite a little boy he delighted in arithmetic, and used to do 
long sums for. his amusement by means of little pebbles 
which he arranged in groups. Once when he had a severe 
illness his mother took the stones away, but, having left him 
alone one day for a little time, she found on her return that 



370 NINETEENTH CENTURY. pt. in 

he had broken his biscuit into little bits and was using them 
to work with instead of his lost pebbles. As he grew older 
his father began to teach him Latin, but the boy disliked it 
so much that it was given up, and he devoted all his time 
to Algebra and Euclid. 

One day he persuaded his father to take him to his friend, 
the Abbe Daburon, to borrow the writings of Euler and 
Bernouilli, two great mathematicians. The Abbe stared 
at this little boy, only twelve years old, asking for books 
which very few men could understand. * Do you know, my 
little fellow,' said he, ' that these works are written in Latin, 
and that the differential calculus is used in them ?' Andre's 
countenance fell for a moment, for he knew neither of these 
things. But he soon brightened up again. * Never mind,' 
he replied, ' I can learn them,' and he set to work that very 
day to learn Latin with his father, and the differential calculus 
with the Abbe, and in a few months was able to come back 
for the books he coveted. 

Before he was eighteen he had not only read the whole 
of Laplace's ' Mecanique Celeste,' but had even worked out 
all the complicated problems in it. He had, however, over- 
taxed his brain, and when his father was killed in the terrible 
French Revolution of 1 7 93, the grief broke down his intellect. 
For a whole year he was almost an idiot, and it was a long 
time before he could take up his mathematical studies again. 
When he did, it was with his old love of work, and he be- 
came a teacher first at Lyons, and afterwards in Paris. 

Ampere's Experiments in Magnetism and Elec- 
tricity, 1820. — This was the man who heard of Oersted's 
discovery in 1820. You can imagine the delight with 
which he seized upon the new idea. He worked at it 
incessantly, as he had done with his pebbles when a boy, 
and before a week was over he had proved several new 



CH. XXXVI. 



AMPERES EXPERIMENTS, 



371 



facts about electro-magnetism. He found that it was quite 
true, as Oersted had said, that the magnet always lies across 
the electric current ; but he showed that the north pole of 
the magnet turns different ways, according to the direction 
in which the current flows. Thus, if the current 1 flows 
from south to north above the magnet, in the direction a b, 
Fig. 64, then the north pole of the magnet turns towards 
the west ; but if it runs from north to south above the 
magnet, in the direction a b, Fig. 65, then the north pole 
turns towards the east. Again, if it runs from north to south 
below the magnet, in the direction c d, Fig. 64, the magnet 



M " 




^K 



Fig. 64. Fig. 65. 

Diagrams showing the direction of a Magnet acted upon by Electric Currents. 

abed, Direction of current. 

will again turn to the west ; while lastly, if it runs from 
south to ?iorth below the magnet, c d, Fig. 65, the north pole 
turns again to the east. In order to remember these differ- 
ent directions easily, Ampere gave something like the follow- 
ing rule. If a man will imagine himself to be standing so 
that the positive current would come out of his mouth and 
return by his feet, the north pole of the magnet will always 
be on his left-hand side. 






1 To avoid confusion, the current from the positive pole of the 
battery is always spoken of as the current. 



372 NINETEENTH CENTURY. ft. hi. 

Lines of Magnetic Force between two Electric 
Wires. — The next discovery which Ampere made was a 
very important one. It was already well known that two 
magnetic needles will either attract or repel each other 
according to the position of their poles. Thus, if the north 
pole of one needle is held towards the south pole of another, 
they are attracted strongly together, but if the two north 
poles are brought near together, the movable needle is re- 
pelled. Now Ampere argued that if an electric current 
always exerts a magnetic action around itself, then two 
electric wires side by side will act magnetically upon each 
other, or, in other words, will attract or repel each other as 
if real magnets were lying between them. And this he 
proved to be true. He put two wires side by side in such 
a position that they could move freely, and when he sent 
an electric current in the same direction through each of 
them they moved towards each other ; while, if he sent the 
currents one way through one wire and the other way 
through the other, they drew apart ; exactly in the same 
way as magnets attract or repel each other, according to 
the direction in which they lie. 

This may be difficult to understand without more expla- 
nation, but you can remember that Ampere proved that 
electric currents exert a magnetic force at right angles to 
themselves in the air without needing any bar of steel to help 
them. 

Electro - magnets made toy means of an Electric 
Current. — It now occurred to Ampere that if electric cur- 
rents give rise to magnetic force he ought to be able to 
magnetise a steel bar by passing an electric current round it. 
So he wound a copper wire (covered with silk to prevent the 
electricity running into the steel) round a steel bar, and, 
fastening the two ends of wire to a voltaic battery, he passed 



CH. xxxvi. ELECTRO-MAGNETS. 373 

a current through it (see Fig. 66). After a short time he 
took the bar out and found it was a perfect bar magnet, 
which would attract iron. The current of electricity, in 
circulating round the steel, had magnetised the steel just as 
if it had been rubbed on a loadstone. 

With steel the magnetism remained after it was taken out 
of the electric coil, but if he used a piece of ordinary soft 
iron the magnetism passed away when the current ceased. 
He called these magnetised bars electro-magnets, because 
they are made by electricity. You can easily make them 
for yourself if you have a small electric battery, and you 
will find that an iron rod will hold up needles, nails, or even 
keys as long as the current is passing, but they will all fall 



Fig. 66. 
Coil of Copper Wire conveying an Electric Current round a Steel Bar. 

off soon after it stops, showing that it is the electric current 
which causes the iron to act as a magnet. 

Professor Arago, whom we mentioned before (p. 324) as 
making experiments on light, succeeded in magnetising a 
steel bar with currents from an ordinary electrical machine, 
that is, a glass cylinder rubbed against silk, instead of using 
a battery. 

Michael Faraday, 1791-1867. — We must now travel 
back to England, where one of our greatest philosophers was 
watching these new discoveries with intense interest. Michael 
Faraday, the son of a poor journeyman blacksmith, was born 
at Newington Butts in 1791. When he was thirteen years 
old he went as errand boy to a bookseller named Riebau 
in Blandford Street, Manchester Square, and it was there that 
the books fell into his hands which first awoke his love 
of science. Mrs. Marcet's ' Conversations on Chemistry,' 



374 NINETEENTH CENTURY. pt. iil 

Lyons's * Experiments on Electricity,' and other books of a 
like kind made the lad long for more knowledge about these 
wonderful sciences. He constructed an electrical machine, 
and spent his evenings in making experiments, and he per- 
suaded his brother Robert to pay a few shillings for him to 
attend some lectures given by a Mr. Tatum on Natural 
Philosophy. 

But one of the first great pleasures of his life was when 
a customer at the bookshop, a Mr. Dance, took him to foui 
lectures at the Royal Institution, given by Sir Humphry 
Davy. These lectures filled him with an intense longing to 
learn more, and he took the bold step of writing a letter to 
Davy, enclosing the notes which he had made of the lectures, 
and asking for some employment connected with science. It 
will always be remembered to Davy's honour that he did not 
throw this letter aside, but wrote a kind reply, telling the 
young man to come and see him, and in the end made him 
his assistant at the Royal Institution in Albemarle Street, 
where Faraday afterwards became Professor of Chemistry. 

It is impossible in a short sketch to give you any idea of 
the simple and noble nature of the man who from that time 
for more than fifty years laboured at science in the Royal 
Institution. It is not yet many years since he died, and you 
may talk with those who have known and loved him, or 
read the story of his life in a little book called ' Michael 
Faraday,' written by Dr. Gladstone. Even of his experi- 
ments we can only mention a few, for these subjects are 
becoming almost too deep for us ; but those which we must 
now consider were some which have helped to make his 
name famous. 

Faraday discovers the Mutual notation of Magnets 
and Electrified Wires, 1821. — It was in 182 1 that Fara- 
day began to repeat for himself Ampere's experiments on 



CH. XXXVI. 



FAR AD A Y'S EXPERIMENTS. 



375 



electricity and magnetism, and he soon saw that if an electric 
current going round a wire gave rise to magnetic action at 
right angles to it, he ought to be able to make an electric 
wire revolve round a magnet, and a magnet round an elec- 
tric wire. Accordingly, he took two cups of mercury, a b, 
Fig. 67, and drilling a hole in the bottom of each, he 
passed the wires e, e, of a battery up into them ; then he 
took two magnets d, d'; d he fastened by a thin thread to 
the battery wire in the cup a, so that it floated upright in 




Fig. 67. 
Faraday's Experiments on the Rotation of a Magnet and of an Electric Wire. 

A B, Section of cups of mercury, c, Copper rod. The current coming in at e passes 
up through the mercury in a, and along the rod c down into the mercury in b, 
and back by e to the battery. On its way it causes the floating magnet, d, to 
revolve round the rod, /, and the loose wire, /', to revolve round the fixed 
magnet, d'. 

K 

the mercury, and the top of it could move round easily ; the 
other magnet, d\ he fixed firmly upright in the cup b. He 
then hung the copper rod c above the cups, so that the end 
/, which was fixed, dipped into the cup a, and the other 
end, which was made of a loose movable wire, /', dipped 
into the cup b. Thus in a the magnet was free to move 



376 



NINETEENTH CENTURY. 



PT. III. 



and the wire was fixed, while in b the wire was free to move 
and the magnet was fixed. He now sent a current through 
the wires, e, <?, and immediately in the cup a the magnet d 
began to move round the fixed wire/, while in b the wire/' 
moved round the fixed magnet, d'. Thus Faraday gave 
fresh experimental proof of the close connection between 
electricity and magnetism. He made the magnet go a 
great way round the circle, but not spin quite round as 
the wire had done. Ampere, however, who repeated the 
experiment, succeeded in making the magnet spin round 
and round like the hands of a clock. 

Electric Current produced by Means of a Magnet. 
Faraday's mind was now full of the wonderful effect which 




Faraday's Experiment on creating an Electric Current by means of a Magnet (Ganot). 

a, Coil of wire round a wooden cylinder connected at the two ends with b, a galvano- 
meter, the needle of which shows directly a curient passes through the wire ; c, a 
powerful magnet. 

electricity and magnetism produce on each other, and he 
began to consider whether it might not be possible to reverse 
Ampere's second experiment (p. 373), and instead of making 






ch. xxxvi. THERMO ELECTRICITY. 377 

a magnet by means of an electric current, whether he might 
not set up an electric current by means of a magnet. 

To try this he wound from 200 to 300 yards of wire 
round a hollow cylinder a, Fig. 68, and carried the two 
ends of the wire to a little instrument b, called a galvano- 
meter, which was invented 'by Ampere, and the needle of 
which moves directly the slighest current passes through it. 
He then took a powerful bar magnet, c, and held it within the 
cylinder. The moment he put it in, the needle of the galvano- 
meter showed that an electric current had passed through 
the wire in one direction, and the moment he drew it out 
another rush of electricity occurred in the other direction, 
showing that the magnet had set up an electric current in a 
coil of wire. While the magnet remained in the cylinder 
there was no current ; it was only at the moment of going 
in and coming out that it produced the effect. By another 
piece of apparatus Faraday succeeded in making these 
currents strong enough to produce electric sparks ; and it is^ 
on this principle that the induction-coil is made which is now 
used to produce very powerful electrical effects. 

Professer Seebeck discovers Thermo-electricity, 
or the Production of Electricity by Heat. — The con- 
nection was now clearly established between currents of 
electricity and lines of magnetic action, and this gives to a 
certain extent the answer to our question, Why does a 
magnet turn to the north ? Ampere suggested quite early 
in the discussion, that if an electric current will turn metals 
into magnets, the electric currents which we know are flow- 
ing from east to west round our globe may turn the earth 
(which is full of metals) into a great magnet. But it is also 
true that exactly the opposite effect is possible, and that the 
lines of magnetic force may be started by some other cause 
and may set up the electric currents, so that we do not 
really know which gives rise to the other. 



-< 




378 NINETEENTH CENTURY. ft. hi. 

An interesting discovery was, however, made in 1822 by 
Professor Seebeck, showing a possible cause of the electric 
currents flowing from east to west. He wished to try whether 
he could not give rise to a current of electricity in two metals 
by merely using heat instead of acid and water. For this 
purpose he took a half ring of copper and fastened to it a 
bar of a metal called antimony, so that the two metals had 
the form of a stirrup, and inside this stirrup he hung a mag- 
netic needle, which would show if any current passed along 
the metals. Then he heated one of the corners where the 
metals joined, and immediately the magnet began to turn, 
showing that an electric current was passing through the 
copper, and back through the antimony. He tried this with 
many other metals, and in every case when one of the parts 
where they joined was made hotter than the rest, a current 
of electricity was caused. This he called Thermo-electricity, 
or electricity caused by heat, and this subject has now been 
much more fully worked out by Peltier and Becquerel on 
the Continent, and Sir W. Thomson, Professor Tait and 
Clerk-Maxwell in England. Thermo-electricity gives us 
another beautiful instance of the transformation of energy. 
We saw in Chapter XXXV. that heat, when it disappears, 
produces a certain definite amount of energy, which again, 
in its turn, can appear in the form of heat ; since then we 
have learnt that electricity gives rise to lines of magnetic 
force, and a magnet sets up an electric current, and now 
we have heat in its turn giving rise to an electric current, 
while we know from the electric spark that chemical action 
can be conveyed by electricity to great distances and then 
made to reappear as light and heat. 

But to turn to the magnet. Seebeck's experiment sug- 
gests a possible answer to the direction of the magnetic 
needle to the north. Our globe is composed of different 



ch. xxxvi. SUN-SPOTS AND MAGNETISM. 379 

metals and earths, and is always turning round from west to 
east, so that one part after another comes under the heat of 
the sun, and is made hotter than the rest. Therefore, since 
an electric current tends to flow round the circuit when the 
functions of two different metals are kept at different temp- 
eratures, it has been suggested that this may cause the 
electric currents to flow round from east to west, as they 
did through the metals in Seebeck's stirrup, thus inducing 
lines of magnetic force from north to south. There may, 
however, be some closer connection between the sun itself 
and magnetic action (see p. 381). j 

Spots on the Sun, and their effect on the Earth's 
Magnetism, Schwabe and Sabine, 1825-1859. — It was 
mentioned at p. 90 that Galileo and other astronomers of 
the seventeenth century first observed that from time to 
time dark spots appear on the face of the sun. These 
spots were much studied by the astronomers who came 
after Galileo ; but Sir William Herschel was the first to 
suggest, in 1793, that they were caused by the opening of 
bright luminous clouds which float round the sun, and 
break away sometimes in one place and sometimes ii 
another, allowing us to see down through the gap into th< 
body of the sun itself, which has thus the appearance of £ 
dark spot. This is the explanation now received by astrq- 
nomers as most probable, and it accounts for the constant 
appearance and disappearance of the spots. 

In the year 1826, a well-known German astronomer, 
Herr Schwabe, of Dessau (who died in 1874), determined 
to take regular notes of the periods when there were most 
spots to be seen on the face of the sun. Every day during 
twelve years, when the sky was clear enough for him to 
observe the sun, he examined it through his telescope, and 
noted how many spots he could see. 
18 



380 NINETEENTH CENTURY. pt. hi. 

In this way he discovered that there was a regular de- 
ciease in the number of spots for about five years and a 
half, and then during the next five and a half years a gradual 
increase, till they were very numerous indeed. This led him 
to think that the spots went through a complete round or 
cycle of changes in about eleven years ; but as he found it 
difficult to persuade other astronomers of the fact, he 
actually carried on his daily observations for twenty years 
longer, and then, at the end of thirty-four years of daily 
observation, he was able to assert boldly that he had estab- 
lished the truth of his theory. 

He had now kept an account of three periods of eleven 
years. At the beginning of each of these periods the sun 
was for some time smooth and almost free from spots : then 
from year to year they increased, till, at the end of five and 
a half years, as many as fifty or sixty could be seen at one 
time. Then they decreased again till, at the end of another 
five and a half years, the sun's face was comparatively smooth 
and spotless. During the time that Schwabe was studying 
these changes, other men in the different observatories of 
Europe had noticed some remarkable peculiarities about the 
magnetic needle. As long ago as 1 7 2 2, a famous astronomer 
named Graham pointed out that the magnetic needle shifts 
from side to side a little every day as the sun passes from 
one side to the other of the globe. The movement is so 
small that it cannot be seen without very accurate instru- 
ments, but it shows that the sun's course does affect the 
magnet ; and when very careful notes began to be made in 
different observatories, it was noticed that this daily shifting 
was greater some years than others. In 1850 an astronomer 
named Lamont, of Munich, pointed out that the movement 
became greater each year for about five and a half years, 
and then grew less during the same period; this led Sir 



CH. xxxvi. MAGNETIC STORMS, 381 

Edward Sabine to suggest that perhaps the spots on the 
sun had something to do with magnetic phenomena, since 
they both went through a regular cycle of changes in about 
eleven years. 

And now comes a curious proof of the truth of this 
theory. In September 1859, when a famous sun-gazer, 
Mr. Carrington, was observing and measuring the spots on 
the sun, he suddenly noticed a bright spot break out on the 
sun's face ; and fortunately another observer, Mr. Hodgson, 
who was in another part of England, saw this same spot at 
the same moment. The whole time from the appearance 
till the disappearance did not exceed five minutes, but when 
inquiry was made, it was found that the three magnetic 
needles at Kevv, which keep a register of their own move- 
ments, had all been jerked strongly exactly at this time. 
Nor was this all : the magnetic storm passing through our 
atmosphere at that moment set up such strong electric cur- 
rents in the wires of the telegraphs all over the world that 
the signalmen at Washington and Philadelphia received 
severe electric shocks ; a telegraphic apparatus in Norway 
was set on fire, and a stream of electric light followed the 
pen of Bain's electric telegraph, which writes down the 
message on chemically prepared paper. Moreover, beautiful 
auroras were seen in both hemispheres, and these brilliant 
lights are believed to be caused by magnetic currents. The 
magnetic storms on this occasion lasted for several days, 
and there could no longer be any doubt that the sun at a 
distance of nearly 92,000,000 miles can produce a complete 
hurricane of magnetic disturbance on our earth. This con- 
nection of the storms with the sun-spots seems indeed, 
as I have said, to suggest that the sun has the power of 
producing terrestrial magnetism in some more direct way 
than merely through the action of electric currents set 



382 NINETEENTH CENTURY. ft. iil 

up by the varying heat on different parts of the earth. The 
whole subject of electricity and magnetism has been carried 
in the present century far farther than we can attempt to 
follow it here, for mathematical knowledge is necessary in 
order to understand its laws as worked out by Weber and 
Helmholtz in Germany, and Sir W. Thomson and Clerk- 
Maxwell in England. 

Invention of the Electric Telegraph by Wheatstone 
and Cooke, 1837. — We have not room to speak here of 
the electric light, the storage of electricity, and other methods 
by which this marvellous force has been made the servant 
of man. But we can hardly close an account of electricity 
and magnetism without showing how the discovery of 
these two forces has made it possible for our thoughts to 
be carried in a few moments of time to the most distant 
parts of the world. Ever since Volta had shown, in 1800, 
that an electric current can be sent for any distance along a 
wire the two ends of which are joined to the poles of a 
battery, scientific men had speculated whether it might not 
be possible to use this current for making signals at a 
distance. The difficulty was how to make the signs at the 
other end. In 1 8 1 6, Mr. Ronalds, of Hammersmith, hung 
pith-balls on to a wire, which stood out while the current 
was flowing, and fell down again when it ceased ; and many 
other plans were tried, but none succeeded well. 

When Oersted, however, showed in 1 8 1 9 that an electric 
current will cause a magnetic needle to turn from side to 
side, it was clear that here was a means by which signs 
could be made at any distance ; and accordingly we find 
that Ampere, in 1830, proposed to work signals by a magnet, 
and different attempts were made in Europe and America 
to carry out his idea. The first electric telegraph of any 
value was patented by Professor Wheatstone and Mr. Cooke 



CH. xxxvi. ELECTRIC TELEGRAPH. 383 

in June 1837 ; and during the same year Dr. Steinheil, of 
Munich, and Professor Morse, of America, both invented 
telegraphs of rather different kinds. I shall not attempt 
co describe all of these, but only to explain the simplest 
principle of an electric telegraph as it is used in England, 
and to show how it depends upon electricity and magnetism. 

You will see, if you turn back to Figs. 64 and 65, p. 359, 
that when the electric current flowed round one way, a b c 
d, Fig. 64, the north pole of the needle turned to the west ; 
when it flowed round the other way, abed, Fig. 65, the 
north pole turned to the east. Now the signals of the 
electric telegraph depend upon this fact, that the direction 
of the current alters the direction of the magnet. When 
one man wants to send a message to another, he does it by 
sending an electric current from a battery along a telegraph 
wire, so that it passes a magnetic needle either from right 
to left or from left to right. When it flows round one way, 
the needle, even if it is a hundred miles off, turns to the 
right, when it flows round the other way the needle turns 
to the left ; and it is agreed that so many strokes to the 
right mean one letter, and so many to the left another letter, 
and in this way a message can be spelt out, however far off 
the two men may be. 

This is the whole secret of the electric telegraph ; but to 
understand how it works you must follow the explanation of 
the two diagrams (Figs. 69 and 70) very carefully. Suppose 
that a message is going between London and York, four 
things are wanted to convey it : — 1. A battery to produce 
an electric current. 2. A wire to carry the current. 3. A 
galvanometer, that is a box, a, a', holding a magnetic needle 
to make the signs. 4. A little box called a Commutator, 
b, b', in which the position of the wires can be changed so 
as to send the current first one wav and then another. 



;S4 



NINETEENTH CENTURY. 



pt. in. 



i. The battery is an ordinary chemical battery such as 
has already been explained. 

2. The wire is stretched from station to station, resting 
on little earthenware cups to prevent the electricity running 
down the poles into the earth, and is arranged in a coil round 
the magnetic needle at each station in such a way that when 
the current flows from left to right the needle will turn to 
the right, when it flows from right to left the needle will turn 




, ... , E /' fit T H r- 



[ ilMWill y 




Fig. 69. 




I&r 




fffiiiiiii 



Fig. 70. 
Diagrams showing the general principle of the Electric Telegraph. 
A, a', Galvanometer, or box containing the magnetic needle. B, b', Commutator, or 
box in which the telegraph wire and earth wire are joined to each other as in b', 
or to the battery, as in B. c, d, Telegraph wire, e, Earth wire. /, g, Copper 
plates at the end of the earth wire. The arrows shew the direction of the positive 
current. 



to the left. You will observe that there is only one wire in 
the diagram, although we know that no current will pass 
unless there is a complete circuit from the battery, going 
out at one pole and coming back to the other. At first 



ch. xxxvi. ELECTRIC TELEGRAPH. 385 

telegraphs were made with a second wire to return the 
current, but Steinheil discovered that this is not needed, 
for that, if the ends of the wires are sunk in the ground, 
with plates of copper,/^-, fastened to them, the earth itself 
will act as the second wire and carry back the return 
current to the battery. It is not known precisely how the 
current returns ; it has been suggested that the earth is a 
great reservoir, as it were, of electricity, so that when the 
current runs into it at one place an equal amount must run 
out at another; but all that is really known is that the 
whole globe acts practically as a return wire. 

3. The magjietic needle is made of tv/o or more parts, for 
since it would be very inconvenient if the pointer were 
always trying to turn to the north, this is avoided by fasten- 
ing two needles side by side, with the north pole of the one 
lying against the south pole of the other, and thus, as the 
earth attracts each needle in a different way, the pull is 
neutralised. This double needle is called an astatic needle, 
and in the form of telegraph we are describing, it is placed 
in the box a, and surrounded by the wire, while a light 
strip of whalebone outside the box is so fastened as to show 
on the face of the dial how the needle is pointing inside. 

4. The commutator, b, is a box with an apparatus inside 
which is so arranged that by turning a handle (not shown 
in the diagram) different ways, the earth wire and telegraph 
wire can be joined together, or either of them can be joined 
to one of the poles of the battery. 

The commutator and galvanometer are really made in 
one instrument, but I have drawn them separate to make 
it more clear. 

Now, when the man in London wants to send his mes- 
sage to York, he first sends off a current which rings a little 
bell at all the stations along the line to call attention, and 



3S6 NINETEENTH CENTURY. pt. hi. 

then spells out the word York. This warns the man at 
that station to turn the handle of his commutator, b', so that 
the telegraph-wire, d, and the earth-wire, g, are joined to- 
gether. Then the message can be sent. The man in 
London' turns his handle according as he wishes the current 
to go. In Fig. 69 he has turned it so that the telegraph 
wire, e, is joined to the positive pole of the battery, and the 
current will pass above ground along c d to the galvano- 
meter a', turning the needle to the right, and will then go 
back into the earth, and an equal amount is restored zXfe 
to the battery. But in Fig. 70 the man has altered the 
handle, and now the earth-wire, e, is joined to the positive 
pole, and so the current passes underground at ef, and out 
at g, and entering the galvanometer on the left side, turns 
the needle to the left, and goes back by the telegraph wire, 
d c, to the battery. In this way he turns it from right to 
left as he will, and spells out the message thus : Left, right 
7 = A ; left, right, left, left, J^ = L ; left, right, right J / = W ; 
left, \ = E; therefore J; Jj J+;J/: \; J+; Jy, spells 
' all wclll 

It is not necessary to have a separate wire for every tele- 
graphic station : one wire will do all the work so long as it 
is only used by one man at a time, and it has now indeed 
been found possible to send two separate messages at the 
same time along one wire. Therefore at every station there 
is a galvanometer to point out the message, a battery to 
provide the current, and a commutator to change the current ; 
but these are not joined to the general wire unless they 
are being used; in Morse's American telegraph, which 
is generally used on the Continent, the needle pricks holes 
in a strip of paper, so that the message can be kept ; Bain's 
electro-chemical telegraph writes down the marks on chemical 
paper; while lately (1879) Mr. Cowper has invented a 



CH. XXXVI. 



THE TELEPHONE. 



387 



telegraphic writing machine, in which the words written at 
one end are reproduced in facsimile by a pen at the other 
end of the wire. But all these are only improvements of 
the same principle by which an electric current going first 
cne way and then another acts on a magnetic needle. 

The Telephone, 1837-1872. — Wonderful as the elec- 
tric telegraph is in its power to send messages almost in- 
stantaneously across the world, yet within the last few years 
an instrument still more wonderful, and at the same time 
even more simple, has been invented. This is the telephone, 
a small instrument which, when fastened to one end of a 





Bell's Telephone. 



Fig. 71. 

2. Section of the same. 



a, Iron plate, b, Soft iron core, c c, Coil of silk-covered wire wound round b. 
d, Permanent magnet, c, e, Connecting wires. 

wire while a similar instrument is fixed at the other end, 
enables us to talk with a person miles distant from us, so 
that he can not only hear the words we say but even recognise 
the tones of our voice. 

As usual many men have helped to bring this instru- 



388 NINETEENTH CENTURY. pt. in. 

ment to perfection. Page in America, de la Rive and Reiss 
on the Continent, and Varley in England, have all made 
attempts to produce speaking at a distance, while Elisha 
Gray of Chicago produced an instrument working with a 
battery, by means of which vocal sounds could be trans- 
mitted. But to Professor Graham Bell of Boston is due 
the credit of having in 1876 at last succeeded in making a 
telephone of the simple construction now used. Fig. 7 1 is 
a drawing of the telephone with a section of it by the side ; 
one of the wires fastened to the end of the instrument is 
carried across the country and fixed at the other end to 
another instrument exactly like it ; the other wire is con- 
nected with the earth. We have seen, p. 376, that Faraday 
was able to produce a powerful electric current in a coil of 
wire by drawing a magnet in and out of the centre of the 
coil. In Bell's telephone a permanent magnet, d, has a piece 
of soft iron, £, fastened to one end of it, and round this soft 
iron is a coil of silk-covered copper wire, At a little dis- 
tance from the soft iron bar is placed an iron plate, a, with 
an opening above it in the wooden case enclosing it, and 
into this opening the person speaks. The vibrations of the 
voice make the particles of the iron plate or diaphragm 
vibrate, so that the plate does not move up and down as a 
whole, but more probably quivers, as it were, throughout its 
whole surface. This vibration affects the soft iron bar, which, 
it must be remembered, is not a permanent magnet, but only 
made so by touching the permanent magnet below. So the 
magnetisation of the soft iron is altered at every sound 
according to the rate at which it vibrates and the form of 
the vibration. This alteration at once sets up electric cur- 
rents in the coil of wire c, and these pass along the wire 
instantaneously to the person at the other end, even if they 
are miles away. This person holds an exactly similar 



ch. xxxvi. THE TELEPHONE. 389 

telephone to his ear. The currents pass into the coil r, 
affect the soft iron b, and make the iron plate a vibrate 
exactly in the same way as the similar plate did at the speak- 
ing end. So the same sounds are returned to the air at 
exactly the same rate and of the same form as the sounds 
caused by the voice at the other end, and we hear the very 
tone of our friend's voice, not because the sound vibrations 
have travelled, but because these have been changed into 
electric currents at one end, and they are changed back 
again into sound at the other. There are many difficulties 
still about the working of the telephone ; other noises some- 
times interfere with the wire and make confusion, and the 
currents are so weak that a very little disturbance prevents 
their acting properly, but numerous improvements have 
been made ever since the above passage was written in 
1879, and there are already many kinds constructed very 
differently from the one I have described. Mr. Edison, 
the well-known inventor in America, has now constructed 
a carbon telephone which, when it is put in the circuit of 
a battery, enables words uttered 115 miles distant to be 
heard easily by a large audience, and the time may come 
when speeches made in London may be listened to by 
crowded meetings in all parts of England. 



Chief Works consulted. — Lardner's 'Cyclopaedia' — 'Electricity, 
Magnetism, and Meteorology;' 'Annals of Philosophy,' New Series, 
1822, vols. ii. and iii. ; 'History of Magnetism ; ' 'Encyclopaedia Me- 
tropolitana,' art. 'Electro-Magnetism;' Faraday's 'Experimental Re- 
searches in Electricity,' 1859; Tyndall's ' Faraday as a Discoverer ;' 
Gladstone's 'Michael Faraday;' ' Nouvelle Biog. Universelle' — 'Am- 
pere,' 'Oersted ;' Ampere, 'Observations Electro-dynamiques,' 1822 ; 
Faraday, 'Various Forces of Nature ;' Proctor, 'The Sun;' Herschel's 
'Familiar Lectures;' Brande's 'Manual of Chemistry ;' Preece On 
the Telephone, ' Nature,' vol. xvi. p. 403. 






390 NINETEENTH CENTURY. pt. hi. 



CHAPTER XXXVII. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Sir Humphry Davy — Laughing-gas — Safety-lamp, 18x5 — Electrolysis 
— Nicholson and Carlisle — Faraday — John Dalton — Law of Mul- 
tiple Proportions — Atomic Theory — Meta-elements — Liquefaction 
of permanent Gases — Liebig — Organic Chemistry — Aniline Dyes. 

Sir Humphry Davy, 1778-1829. — We saw in the last 
chapter how Oersted, Davy, Ampere, Faraday, and Seebeck, 
by their various discoveries, showed the connection between 
Electricity, Magnetism and Heat. We must now learn how 
the connection between electricity and chemical change was 
also worked out. This was done by Sir Humphry Davy 
and Faraday, who thus put England once more at the head 
of chemical discovery, in which the French school of Lavoisier 
had so long taken the lead. 

Sir Humphry Davy, whom we have mentioned before as 
making experiments upon heat, was born in 1778, at Pen- 
zance, in Cornwall, and died at Geneva in 1829. His 
mother being a widow, he was apprenticed when quite young 
to an apothecary, and there with wine glasses, old medicine 
bottles, tobacco pipes, and a syringe, he made his first 
chemical experiments. When he was scarcely twenty years 
of age, Dr. Beddoes, a physician, who had opened a hospital 
for curing patients by the use of different gases, heard so 
much of the young man's abilities that he invited him to 
come to Bristol, where he employed him in making experi- 
ments. 



ch. xxxvii. SIR HUMPHRY DAVY. 391 

In this way Davy's attention was drawn to nitrous oxide, 
a gas which had been declared by a celebrated physician, 
Dr. Mitchell, to be very poisonous. Our young chemist 
wanted to try this for himself, and actually began breathing 
it in small quantities to see whether it would affect him. 
He proved that it certainly was not so poisonous as Mitchell 
had thought, and, growing gradually bolder and bolder in 
the use of it, he succeeded at last in breathing the gas for 
several minutes, at the end of which time he lost all con- 
sciousness, and found himself in a land of delicious dreams, 
out of which he awoke gradually without being injured in 
any way. Enchanted at having discovered such a delightful 
sensation, he carried on his experiments for more than ten 
months, and when he published the results, and told the 
world that the mere breathing of a gas could make a man 
sleep, and dream, and laugh without any cause, it created 
a great sensation, and Davy's name soon became well 
known. 

At this time (1801) the Royal Institution had just been 
founded, and Count Rumford, seeing that Davy was a young 
man of great talent, offered him the appointment of Assistant- 
chemist. Davy accepted it, and from that time devoted 
himself entirely to science. He was young, bright, and 
enthusiastic, and his lectures were so clear and eloquent, 
that the Royal Institution soon became famous under his 
influence, while every new appliance for making chemical 
experiments was given him in his laboratory. It was here 
that he made his observations on flame in 18 15, and con- 
structed his Safety-lamp, which has saved so many lives, and 
for the invention of which he received the title of baronet. 
It was here also that he made his first experiments in electro- 
chemistry, which is the only one of his many discoveries of 
which we can speak. 



392 NINETEENTH CENTURY. rr. in. 

Discovery of Electrolysis, or the Decomposition of 
Substances by Electric Currents, 1800-1806. — In the 

year 1800, two men nnmcd Nicholson and Carlisle discovered 
by chance that when the two wires of a voltaic battery were 
dipped in water, bubbles of gas rose up from them. They 
also found by experiment that the gas from one wire was 
oxygen, and from the other hydrogen ; but where these gases 
came from, whether they were produced by the electricity, 
or came from the battery, or from the water, they could not 
tell. Moreover, besides the oxygen and hydrogen which 
came off, there also appeared an acid of some kind at the 
positive pole, as was shown by damp litmus paper turning 
red (see p." 228), and an alkali appeared at the negative 
pole which turned this red litmus paper blue again. This 
looked as if the electric current had produced something in 
the water ; for Cavendish, as you will remember, had shown 
that pure water is made of oxygen and hydrogen only (see 
p. 230). Many chemists, therefore, set themselves to try 
to discover what effect the electric current had on the water, 
and Davy in 1806 succeeded in solving the question. 

The history of his experiments is especially interesting, 
because it shows, as we have noticed so often before, that a 
patient and careful inquiry into nature always gains a true 
answer in the end. Davy did not believe that the electric 
current produced anything in the water; he thought that 
both the acid and the alkali came from the vessels that were 
used. So he set to work steadily to clear away all possibility 
of impurities. He took distilled water, and used cups first 
made of agate, and afterwards of pure gold, because he 
found that the clay of the china cups was acted upon by the 
current. Yet, in spite of these and many other precautions, 
the acid and the alkali still continued to appear. Then he 
used water which he had evaporated very slowly, instead 



en. xxxvii. ELECTROLYSIS. 393 



of distilling it, because he found that distilled water carried 
away some salt with it. When he had done this the acid 
was weaker, but the alkali was as strong as ever. At this 
point it occurred to him that the alkali might perhaps come 
out of the air, so he put his gold cups of water under an 
air-pump, and completely exhausted the air, filling the pump 
with hydrogen to make quite sure that no other gas could 
be left in. When he had tried this several times and made 
it perfect in every way, he succeeded at last in getting nearly 
pure oxygen at one pole and hydrogen at the other, while the 
water decreased in the cups. 

By this experiment Davy not only confirmed Cavendish's 
discovery that pure water contains nothing but hydrogen and 
oxygen, but he also established a totally new method of 
analysing substances, and finding out the materials of which 
they are composed. This method was in some ways more 
certain than Bergmann's method of tests, for when you drive 
one element out by putting another in its place, you have 
some difficulty in finding out exactly what has happened ; but 
when a substance is decomposed by electricity you literally 
take it to pieces, and see the elements of which it consists. 

Discovery of Potassium and Sodium. — Having suc- 
ceeded in the case of water, Davy now went on to try the 
effect of the electric current on other bodies, and the first which 
he took were common potash and soda, which had always been 
supposed to be simple substances, which could not be decom- . 
posed. For several reasons, however, Davy believed that it 
would be possible to reduce them into more than one sub- 
stance. So he heated some pure potash in a spoon until it 
was quite liquid, and fastening the two ends of the spoon to 
the wires of a battery, he sent an electric current through it. 
After a little while the potash began to be agitated, and to rise 
up in bubbles, and then there came to the surface beautiful 



394 NINETEENTH CENTURY. pt. lit. 



silver-like globules, some of which burst into flame, while 
others remained covered by a sort of white film. 

c Davy's delight,' writes his brother, ' when he saw the 
minute shining globules like mercury burst through the crust 
of potash and take fire as they reached the air, was so great 
that he could not contain his joy — he actually bounded 
about the room in ecstatic delight.' It must indeed have 
been a beautiful sight in itself; but probably Davy's excite- 
ment arose chiefly from the new truth he saw in it He had 
proved that potash was not a simple substance, but contained 
something which had never before been discovered. 

At first he had great difficulty in collecting the globules, 
for they not only burst into flame when they met the air, 
but even in water they took fire, joining themselves to the 
oxygen and setting the hydrogen free. At last, however, he 
succeeded in collecting them in rock oil, or naphtha, which 
contains no oxygen. He was then able to examine them, 
and he found they were composed of a metal hitherto quite 
unknown, to which he gave the name of potassium. A few 
days later he procured the metal sodium out of common 
soda by the same process. 

This method of decomposing substances is called electro- 
lysis, which means ' setting free by electricity.' Davy made 
use of it to decompose many earths, such as lime, magnesia, 
etc., and the great Swedish chemist, Berzelius (born 1778 
died 1848), discovered several new chemical substances by 
means of it. 

Faraday's Experiments on the Connection between 
Electricity and Chemical Affinity.— The power of de- 
composing substances was the practical benefit obtained 
by the discovery; but it had another great interest for 
chemists, because it proved that electricity can overcome 
that power called ' chemical affinity,' which holds two 01 



ch. xxxvii. ELECTRICITY 6- CHEMICAL AFFINITY. 395 

more elements together in one compound substance. You 
will remember that Bergmann, and indeed Newton before 
him, pointed out that there is some force which causes 
certain bodies to choose each other out when they meet, 
and to unite firmly so as to become a new substance which 
has its own peculiar characters. Chlorine and sodium, for 
example, when heated, unite to form common salt, which is 
not the least like either chlorine or sodium when they are 
separate ; and in the same way hydrogen and oxygen unite 
to form water. In these new states they are held together 
by a power which for want of a better name we call 
' chemical attraction,' or ' chemical affinity.' 

Now Davy showed that an electric current conquers this 
power and sets the different elements free, so that they can 
each go their own way. Thus the electric current passing 
through the water overcomes the force which holds the 
oxygen and hydrogen together, so that, at the point where 
the battery wires touch the water, hydrogen bubbles come 
off on one side and oxygen on the other. 

It is to Faraday, however, that we owe most of our 
knowledge about the intimate connection between electricity 
and chemical change. He followed Davy's experiments, 
and traced out very clearly the cause and effect of the 
chemical current. He showed in the first place that a sub- 
stance cannot be decomposed by electricity unless it is a 
good conductor, so that the current passes readily along it. 
Thus, ice being a bad conductor, the slightest film of ice 
interposed between the water and the electric wires will pre- 
vent the current from setting free the oxygen and hydrogen ; 
and ether and alcohol cannot be decomposed at all by elec- 
tricity, because they will not conduct the current. 

He also showed that the electric current itself does not 
depend upon any effect which the two metals have directly 



396 NINETEENTH CENTURY. PT. ill. 

upon each other, -as Volta thought, but is caused by the 
chemical action going on between the zinc and the water. 
'I hus, if you put some zinc in sulphuric acid and water, the 
zinc pulls the water to pieces, and hydrogen gas comes 
bubbling off, but if you coat the zinc with mercury, hydrogen 
will no longer come off, and no action will take place till 
you put another metal in the water, as for example a piece 
of copper, and connect the two metals by a wire. Then the 
hydrogen bubbles off again, but this time it does not come 
off the zinc, but off the copper. The force which overcomes 
the chemical attraction in the water has been made to travel 
across the vessel from one metal to the other, and this 
journey may be made as long a one as you choose, and may 
even be continued for hundreds of miles if only the current 
has some means of finding its way home to the first metal 
at last. 

Now all this is a modified result of the chemical action 
of the zinc and acid water upon each other ; as Faraday 
proved in a most beautiful way by showing that the power 
of the electric current to decompose water in another vessel 
depends entirely upon the violence of the action going on 
between these two elements of the battery. If the battery 
is weak, the water in which the ends of the wires are dipped 
is decomposed slowly; if the battery is strong, the bubbles 
of oxygen and hydrogen come off rapidly and vehemently. 
This led him to invent a useful little instrument called a 
volta?neter i which measures the quantity of water decom- 
posed, and so tells exactly what is the strength of the electric 
current. * Thus we see,' says Faraday in one of his lectures, 
1 that the power which decomposes water, or produces the 
heat and light of the electric spark, is neither more nor less 
than the chemical force of the zinc — its very force carried 
along the wires and conveyed to another place.' 



en. xxxvu. CHEMICAL METHODS. 397 

- - — — — — — ^=v 

And here again we find ourselves brought face to face! 
with the truth that all the various physical forces are only 
different forms of one and the same force. We learnt be- 
fore that mechanical energy can be turned into heat, and 
heat into mechanical energy, while heat, magnetism, and 
electricity all in the same way give rise to each other ; and 
now we learn that chemical change gives rise to electricity, 
and electricity in its turn to chemical change. So that the 
whole set of physical forces, heat, electricity, magnetism, 
and chemical change, are all different phases of the same 
indestructible energy which we lose sight of in one shape, 
only to find it in another. 

Methods of Studying Chemistry. — We have now 
learnt how most of the chief methods of producing chemical 
change have been worked out. The science of chemistry 
consists in using these methods to test and decompose all 
the substances in our earth and atmosphere, and so learning 
their nature. 

We have seen that there are four ways of thus analysing 
compound bodies. First, by testing them with other sub- 
stances which attract some of their elements, and draw these 
out of the compound, as when by plunging a piece of iron 
into nitrate of copper the iron attracts the nitric acid and 
draws it out, leaving the copper to fall down as a metal. 
This was the method chiefly worked out by Bergmann in 
1 76 1, and which has since then been brought to much 
greater perfection by other chemists. 

Secondly, by heating substances gently and examining 
the vapours which rise from them, and afterwards analysing \ 
what remains by burning. This method was fairly under- | 
stood by Geber, and was first applied to organic substances J 
by Boerhaave. 

Thirdly, by passing an electric current through a com- 






398 NINETEENTH CENTURY. PT. in. 

pound substance m a fluid state, and so overcoming the 
force which holds the different elements together and 
setting them free. This method, called electrolysis, was dis- 
covered by Davy in 1 806, and afterwards thoroughly worked 
out by Faraday. 

Fourthly, there is the method of spectrum analysis 
suggested by Herschel in 1822, which was carried on with 
great success by Bunsen and Kirchhoff. In this method 
the substance is turned into gas either by ordinary heat or 
by the electric spark, and is then examined by the spectro- 
scope ; the elements being determined by the position of 
the bright lines they throw on the spectrum. 

There is still a fifth method, about which we have said 
nothing as yet, and which was chiefly brought into use by 
the chemist Berzelius, namely the fusing of substances by 
means of the blowpipe. This instrument is merely a little 
tube with a mouthpiece at one end and a very minute hole 
at the other. By placing the minute hole in the middle 
of a flame and blowing through the mouthpiece, the centre 
of the flame is made to burn furiously, and many sub- 
stances can be melted and decomposed by it which do not 
yield to ordinary heat. 

By these different methods a very large number of sub- 
stances have been analysed since the time of Davy and 
Faraday, and seventy elements or simple substances have 
been discovered. It is possible that some of these may 
even at some future time be decomposed and shown to be 
made up of two elements ; we can only affirm that now they 
appear to us to be simple substances. Some of these 
elements have been brought together and made to unite 
into compound substances by artificial means ; as when, 
for instance, oxygen and hydrogen mixed and lighted by 
a spark rush together and form water, or when hydrogen 



CH. xxxvii. JOHN DALTON. 399 

r 

/ 

and chlorine mixed together and placed in the sunlight 
unite to form hydrochloric acid. 1 This method of bringing 
elements together to form a compound substance is called 
synthesis, and is exactly the opposite of analysis, or the 
splitting up of a compound substance into its elementary 
parts. 

To follow out the gradual development of synthesis and 
analysis, and the discoveries of our great modern chemists, 
such as Graham, Andrews, and others, would be to write a 
work upon chemistry. There is only one other general prin- 
ciple which we ought to try and understand here ; namely, 
the proportions in which the elements combine to form sub- 
stances. This principle, which lies at the root of all our 
modern chemistry, was first worked out by a poor school- 
master named Dalton. 

Dalton shows that the Different Chemical Elements 
always Combine in Definite Proportions. — John Dalton 
was born of Quaker parents in 1766, near Cockermouth, in 
Cumberland. He received the ordinary education of a 
village school, and after being master of a small academy 
at Kendal, he went to Manchester, where he supported 
himself all the rest of his life by teaching mathematics. 
Fortunately for science, a blind gentleman named Gough 
became interested in him, and gave him the use of his 
library and chemical laboratory, which enabled Dalton to 
work out many useful facts, and to establish the laws which 
are now the guide of all chemists, though they differ about 
some of his conclusions. 

You will remember that it was only in the time of 
Lavoisier that chemists began to weigh carefully the gases 

1 Sir H. Davy was the first to discover, in 1807, that hydrochloric 
acid is made merely of hydrogen and chlorine ; before then it was 
believed that every acid must have oxygen in it. 



400 NINETEENTH CENTURY. pt. ill. 

into which substances can be decomposed. Before then it 
had been thought sufficient to say that a substance contained 
sulphur, mercury, carbon, etc., without saying how much of 
it there was. But after the discovery of oxygen, when the 
real nature of chemical change began to be understood, 
chemists saw the importance of weighing accurately the 
different elements into which a substance can be broken 
up ; and when this had been done for some time, and a 
great number of analyses had been made, it was seen that 
any given chemical compound always contains the same elements 
combined in the same proportion. 

Thus, for example, all water, whether it comes from rain, 
snow, dew, steam, or exploded oxygen and hydrogen, will 
always be found to contain two parts by weight of hydrogen 
to sixteen parts by weight of oxygen ; so that if you decom- 
pose 1 8 ounces of water you will collect 

2 volumes of hydrogen weighing I oz. each , . 2 ozs. 

I volume of oxygen weighing 16 ozs. . . 16 ozs. 



is ozs. 



And this never varies. Again, if you take some ammonia 
and decompose 1 7 ounces of it you will collect 

3 volumes of hydrogen weighing I oz. each . . 3 ozs. 

I volume of nitrogen weighing 14 oz. . . . 14 ozs. 



17 ozs. 

And this again never varies. Wherever you get ammonia 
it will always be made up of these proportionate weights of 
hydrogen and nitrogen. 

This combination of the different elements in fixed 
quantities is called the law of definite proportions. It was 
hinted at by four chemists before Dalton \ namely Proust, 
Wenzel, Higgins, and Richter, but it was very little under- 



ch. xxxvii. LAW OF DEFINITE PROPORTIONS. 401 

stood, and some eminent chemists, such as Berthollet, even 
doubted whether it was true. Dalton, however, made a re- 
markable discovery which both proved the truth of the law 
itself and showed that it meant a great deal more than had 
been imagined. 

He found that not only are the elements in any one sub- 
stance always in a fixed proportion, but that each element, 
such as oxygen, has a weight of its own, and will only com- 
bine with other elements in proportions of this fixed weight. 
For example, oxygen will join itself to nitrogen in five dif- 
ferent proportions, making five different substances, and in 
each case the same fixed weight of oxygen is added. Thus, 
if you decompose 2 2 '4. litres of 







Volumes of 


Weighit 


ig 






Nitrogen 


Oxygen 


Nitrogen 




Oxygen 


Nitrous oxide, you 


will 


get 2 . 


. I . 


. 28 grammes 16 grammes 


Nitric oxide 


>> 


2 . 


. 2 . 


. 28 


>> 


32 „ 


Nitrous acid 


»» 


2 . 


• 3 • 


. 28 


>> 


48 „ 


Nitric peroxide 


»» 


2 . 


. 4 • 


. 28 


>» 


64 „ 


Nitric acid 


»> 


2 . 


• 5 • 


. 28 


>» 


80 „ 



So that each substance contains one more volume of oxygen 
compared to the nitrogen than the one before it ; and this 
volume always weighs 16 grammes, while each volume of 
nitrogen weighs 14 grammes. 

Oxygen behaves in this way in all compounds, only join- 
ing itself to other elements in weights of 16 or multiples 
of 1 6. Thus, if you heat mercury as Lavoisier did, so that 
it takes up oxygen out of the air, 200 parts by weight of 
mercury will combine with 1 6 of oxygen and no more. If 
you heat carbon with oxygen, 1 2 parts by weight of carbon 
will take up 1 6 of oxygen to make carbonic oxide, or twice 
16 = 32 to make carbonic acid, but it will not take up any- 
thing between these weights. This same law holds true of 



4Q2 NINETEENTH CENTURY. pt. ill. 

all the elements, each one having its own peculiar weight. 
Nitrogen, for example, combines in weights of 14, or twice 
14 = 28, or three times 14 = 42, etc. ; sodium in weights of 
23, 46. and 69, etc. This is called the law of multiple pro- 
portions, which we owe entirely to Dalton, and it is a fact 
about which all chemists agree. Dalton went on to try and 
explain it by a theory which is still a matter of speculation, 
and which some chemists do not receive. 

Dalton's Atomic Theory, 1808. — In order to explain 
why each element should have its fixed weight in which it 
always combines, Dalton imagined, as Democritus, Epicurus, 
Bacon, and Newton had done before him, that all matter is 
composed of tiny parts, or atoms, which are too small to be 
seen, and which cannot be divided. These atoms, which he 
pictured to himself as round grains like very small shot, 
would be of the same size in every substance, but not of the 
same weight. Hydrogen atoms would be the lightest of 
all, for hydrogen is the lightest substance known ; oxygen 
atoms would be 16 times, and nitrogen 14 times, as heavy 
as those of hydrogen. 

Now when two elements combine together they cannot 
take up less, according to Dalton, than one atom of each, 
or two atoms of one to one of the other, and so on, and 
therefore exactly the weight of an atom of any substance will 
always be added. For example, to turn back to our table 
on p. 389, Dalton would say that a molecule, or the smallest 
portion which can be imagined, of nitrous oxide will contain 
2 atoms of nitrogen weighing 1 4 each to 1 atom of oxygen 
weighing 1 6 ; while nitric acid will contain 2 atoms of nitro- 
gen = 28, and 5 atoms of oxygen, 5 x 16 = 80. If half an 
atom of oxygen could be added, then it might be possible 
to take up 16 + 8, or 24 parts of oxygen ; but as the atoms 
are supposed to be indivisible, this cannot be done, but a 



ch. xxxvu. D ALTON'S ATOMIC THEORY. 4°3 

whole atom weighing 1 6 must be added each time. There- 
fore you will see that by an atom, Dalton meant the smallest 
quantity of any element which can combine with other sub- 
stances. 

Thus, water is made up of molecules, each containing 
two atoms of hydrogen and one of oxygen. But as these 
atoms cannot be seen, how can it be known how many there 
are in any substance, and when we have arrived at the 
smallest weight of any element ? Dalton knew it in some- 
thing like the following way : — 

If you decompose water by electricity, you know that 
you will collect two bottles of hydrogen for one of oxygen. 
But you can also decompose it another way : if you take a 
small piece of the metal sodium and float it on water, it will 
roll round and round fizzing violently. This is because 
sodium joins very readily to oxygen, and the sodium is 
turning out some of the hydrogen from the water and taking 
its place. When the piece of sodium has disappeared, if 
you evaporate off the rest of the water, you will have a white 
powder, which is caustic soda ; and if you decompose this 
soda, you will get out of it one measure of hydrogen, one 
of oxygen, and one of sodium. The sodium, you observe, 
has turned exactly half the hydrogen out of the water and 
taken its place ; and this shows there must have been two 
atoms of hydrogen in the water, because a single atom 
could not have been divided. 

In the soda we have now got the smallest quantity of 
each element — sodium, oxygen, and hydrogen — which will 
combine with any other. You can turn either of these 
three out of the soda, but you cannot turn out a part of 
any one of them. Therefore, a molecule of soda is said to 
be made of one atom of hydrogen weighing i, one atom of 
oxygen weighing 16, one atom of sodium weighing 23, and 
19 



404 NINETEENTH CENTURY. ft. hi. 



these numbers are called the atomic weights of hydrogen, 
oxygen, and sodium. 

This will give you a rough idea of Dalton's theory of 
atoms. There is always this difficulty in it that we cannot be 
quite sure when we have arrived at the smallest quantity of 
any substance ; for suppose that one day we were to find 
that half as much oxygen would unite with some other sub- 
stance as now unites with sodium, then the atom of oxygen 
would no longer weigh 1 6, and for this and other reasons 
atoms are used by chemists merely as convenient units. 
But if we bear this possibility in mind, then the theory is of 
great use in giving us the symbols which are now used in 
chemical language. For when it was once agreed that the 
weight of an atom of hydrogen should be reckoned as i, 
then an atom of oxygen will weigh 1 6, and the letters HHO 
express a great deal. They tell us that two atoms of hydro- 
gen weighing 2 are joined to one atom of oxygen weighing 
16, to form a molecule of water. In the same way HO,NA x 
tells us that single atoms of each of these substances, weigh- 
ing respectively 1, 16, 23, form a molecule of soda. And 
thus a complete chemical language has sprung up, by which 
chemists in all parts of the world can understand at once 
what is the composition of any substance ; and by means of 
these simple letters the most complicated chemical problems 
can be worked out clearly and intelligibly. 

Dalton's theory was received very quickly by chemists, 
considering how entirely new the ideas were which it taught. 
His friend Dr. Thomson, an eminent chemist (born 1773, 
died 1852), gave a very clear account of it in his ' System of 
Chemistry,' and brought it under the notice of Davy and Fara- 
day; and a great French chemist, Gay-Lussac (born 1778, 

1 Na stands for Natrium, the Latin name for soda, now used for 
the metal sodium. 



ch. xxxvu. D ALTON'S ATOMIC THEORY. 405 

died 1850), adopted it at once, and added another discovery 
in favour of it in 1809 — namely, that when substances are 
reduced to gas, and the gas is collected, it is found that the 
different elements combine in equal or multiple volumes. 

You will understand this by turning back to the com- 
pounds of nitrogen and oxygen (p. 401), where you will see 
that there was always either 1, 2, 3, 4, or 5 volumes of 
oxygen collected for one of nitrogen, and never a part of 
a volume. This was really a different fact from the one 
Dalton pointed out, that the elements combine in definite 
weights, and it was necessary to complete the law of mul- 
tiple proportions. In 1 8 1 1 a still further step in advance 
was made by the Italian chemist Avogadro, who showed 
that equal volumes of gases or vapours under the same 
conditions of pressure and temperature contain the same 
number of molecules \ and Ampere brought forward the 
same doctrine in 18 14. These discoveries were followed up 
by Gerhardt, Berzelius, Sainte-Claire, Deville, and others. 

We said at p. 398 that it is possible those bodies which 
we now call elements may not after all prove each one to be 
a simple substance, and in the last few years many new 
theories have been formed on this subject. Mr. Lockyer 
has been led by his study of the spectrum of the sun to 
the opinion that many of the substances which behave as 
elements in our globe are dissociated or split up in the 
fierce solar heat ; while Mr. Crookes, from chemical experi- 
ments, and from the double forms of crystallisation of 
certain elements, concludes that there are some far more 
unstable than others, and he proposes to call these meta- 
elements. There are many difficulties as yet in proving 
either of these hypotheses, but it is well to remember that 
chemists and physicists are both now inclined to question 
the simple nature of many so-called elements. 



4 o6 NINETEENTH CENTURY. pt. iil 

Liquefaction of the Permanent Gases, 1877-8.— 
But though we cannot follow out the more subtle advances 
in chemistry, there is yet one so interesting and important 
that it must be mentioned. In 1823 Faraday first liquefied 
chlorine and several other gases, but oxygen, hydrogen, and 
nitrogen refused to yield to liquefaction, and were therefore 
called 'permanent gases,' and Dr. Andrews of Belfast ex- 
plained the reason why they could not be overcome. 

If we picture to ourselves a gas as being composed of free 
molecules flying about in all directions, we can understand 
that if these are pressed very closely together they may 
come sufficiently near to be held together by cohesion, and 
in fact many gases, such as chlorine, hydrochloric acid, 
and ammonia, can be reduced to liquids merely by being 
compressed at the ordinary temperature of our air, or very 
little below it. But Dr. Andrews has shown that by heating 
liquids we can always arrive at a critical point of tempera- 
ture (differing for different substances), at which no amount 
of pressure will keep them liquid. If we heat a liquid with 
its vapour in a sealed tube, as we arrive near to this par- 
ticular temperature the surface of the liquid loses its natural 
curve in the centre, and flattens more and more, thus show- 
ing that the molecules are held together less and less firmly, 
until at the critical point the force of cohesion loses its 
power altogether, and the whole contents of the tube become 
vapour. In fact, the energy of movement of the molecules 
has become so great that it quite overcomes the attraction 
which each molecule has for the other, and so long as the 
vapour is kept at this temperature, no amount of com- 
pression will force it to become a liquid. Thus, for example, 
carbonic acid at a temperature of 35*5° Cent, may be com- 
pressed under 108 times the weight of our atmosphere, till 
430 pints of it are forced into a vessel only holding one 



ch. xxxvii. LIQUEFACTION OF GASES. 407 

pint, and yet it will remain unliquefied. But directly it is 
reduced below 30*92° Cent, which is its critical point, the 
molecules do not move with sufficient energy to resist 
cohesion, and the vapour becomes liquid at once without 
suddenly changing its volume or giving out any heat. 

Now, those gases, oxygen, hydrogen, and nitrogen, which 
were called ' permanent' gases, have each their 'critical 
point,' so enormously below all ordinary temperatures that 
no one until December 1877 had succeeded in obtaining 
cold and pressure enough to reduce them to liquids. But 
in that month M. Raoul Pictet, of Geneva, and M. Cail- 
letet, an iron-founder at Chatillon sur Seine, were fortunate 
enough to liquefy oxygen, each of them independently of 
the other. 

M. Cailletet put his oxygen in a small tube under 
enormous pressure, surrounded it by a freezing mixture, 
and then let it suddenly escape from the tube. The gas, 
already intensely cold (29° below o° Cent), became so much 
colder by expanding as it rushed out, that it liquefied into 
minute drops, giving the appearance of a mist. M. Pictet 
had a more elaborate apparatus, in which, by a double pro- 
cess of freezing, by means of sulphurous acid and carbonic 
acid, he obtained a cold of 140° Cent, below the freezing 
point, while he exerted a pressure upon the gas 650 times 
greater than the pressure of our atmosphere. He then 
opened the stopcock, and the oxygen, set free, shot out in 
a liquid stream. 

The next step was made by M. Cailletet on the last day 
of 1877, when he compressed not only nitrogen and hydro- 
gen, but also atmospheric air into liquids, before the leading 
scientific men of Paris. The nitrogen appeared in drops, 
but the hydrogen only as a faint mist Lastly, M. Pictet, 
on January 11, 1878, under a pressure 650 times that of 



4 o8 NINETEENTH CENTURY. pt. iil 

our atmosphere, and with a cold of 170 C, obtained a jet 
of liquid hydrogen, which became partly solid and struck on 
the floor with ' the shrill noise of metallic hail,' thus con- 
firming the idea first suggested by Faraday, that hydrogen 
is a metal. These experiments have removed the last 
barrier between gases and vapours, and we now know that 
all substances only require suitable conditions to take either 
of the three forms of solid, liquid, or gas. Thus M. Cail- 
letet and M. Pictet have abolished the belief in ' permanent 
gases.' 

Liebig the Great Teacher in the Chemistry of Or- 
ganic Compounds. — And now, before closing the history 
of chemistry, we must mention, in passing, one great division 
of the science of which we cannot attempt to give any real 
account — namely, the science of organic chemistry, or more 
properly the chemistry of organic compounds. This study 
began, as you will remember, when Boerhaave first examined 
the juices of plants and the fluids in animal bodies. But it 
can scarcely be said to have made any great advance till 
the year 1828, when a German chemist named Wohler first 
showed that urea, a substance in the bodies of animals, can 
be made artificially. Since then Berthelot and other eminent 
chemists who have followed him have discovered how to 
make many compounds in the laboratory which were before 
only found in living beings. 

But the great master of organic chemistry whose name 
you must remember, though we can speak but little about 
him, was Baron Liebig, of Darmstadt, who was born in 
1803 and died in 1873. From the days when he was a 
schoolboy, Liebig had made up his mind to be a chemist, 
and through the kindness of Humboldt he was fortunate 
enough to be introduced to Gay-Lussac, and to work with 
him for some years. In 1824 he was made Professor of 



ch. xxxvu. BARON LIE BIG. 409 

Chemistry at Giessen, where he organised the first great 
chemical laboratory, and for twenty-seven years lectured to 
students from all parts of the world. In 1852 he accepted 
an invitation to Munich, where he remained for the rest of 
his life. He was the first to analyse organic substances 
satisfactorily, by heating them in vessels with metallic oxides, 
thus reducing them to carbon and their other elements;; 
and to show by experiments which he made with Wohler, I 
that there is chemically no sharp line of separation between J 
organic and inorganic matter, for that, however complicated ' 
the components of organic substances may be, they are 
subject to the same chemical laws as the simpler components 
of inorganic matter. He is, however, perhaps best known 
for his great discoveries in agricultural chemistry. This 
subject, which was first treated by Sir H. Davy, teaches how 
the growth of plants depends upon the chemical state of the 
soil in which they are sown, how different crops should be 
sown in succession in any field so as not to exhaust the soil ; 
and what manure will best give back to the ground the 
elements which the plants have taken out of it. Liebig also \ 
traced out the changes which food undergoes in our bodies, / 
and studied which kinds turn to fat, muscle, blood, or sugar 
in our system. In 1832 he also discovered chloroform and^V* 
chlorale, though these were not used for producing uncon--^ 
sciousness till more than fifteen years later by Sir James 
Simpson. 

The whole history of organic chemistry, however, is far 
beyond us at present, though we can understand that it has 
opened the way for a far more real knowledge of the effects 
of drugs, of the working of poisons, of the chemical action 
of food in the body, and of many conditions of health and 
disease : for if the physician can know the actual chemical 
changes produced within the body with great accuracy, he 



4io NINETEENTH CENTURY, PT. in. 

is no longer working in the dark, as he was when he could 
merely judge by outward effects. In quite another branch, 
less important, but still of great interest, the chemistry of 
organic compounds has been most useful. In 1825 Fara- 
day extracted from coal-tar an important substance called 
benzole, and from this a heavy colourless liquid, 'aniline,' 
can be obtained. In 1856 Mr. Perkins discovered that by 
adding hypochlorite of sodium to this liquid a lovely mauve 
colour was^ produced, and this has led to the discovery of 
all the beautiful aniline dyes which are now prepared both 
from living plants and from the coal-tar which comes from 
plants of bygone ages. 

It would be impossible to give a list even of the leading 
chemists of the present day. Wohler, Graebe, Hoffmann, 
Wiirtz, Frankland, and Williamson, are only a few among 
equally illustrious names, and it must yet be many years 
before a fair sketch can be given of the history of the 
chemistry of the organic compounds ; but we may be sure 
that such a future historian will, as Dr. Andrews has said, 
'have to record a succession of beneficent triumphs, in 
which the effects of science have led to results of the highest 
value to the wellbeing of man.' 



Chief Works consulted. — Davy's 'Works,' 1840; Whewell's 'In- 
ductive Sciences;' Dalton's 'Chemical Philosophy,' 1808; Dr. Henry's 
'Memoir of Dalton,' 1854; Fownes's 'Chemistry;' Brande's 'Chem- 
istry;' Faraday's 'Various Forces of Nature;' 'Edinburgh Review,' 
vol. xciv. 'Modern Chemistry;' Hoffmann, 'On Liebig and Fara- 
day;' Liebig's Scientific Attainments, 'Contemporary Review,' April 
1877. 



ch. xxxviii. ADVANCES IN NATURAL SCIENCE. 41 ] 



CHAPTER XXXVIII. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Jussieu on Natural System of Plants — Sprengel on Insect Fertilisation 
— Robert Brown — Goethe on Metamorphosis of Plants. 

The short sketch of advances in modern chemistry given in 
the last chapter brings us to the end of the physical sciences, 
or those which deal more particularly with the properties of 
inorganic substances, and the laws of their action upon each 
other. We must now pass on to those sciences which treat 
of the past and present history of the globe, and the living 
beings which inhabit it. I shall not attempt to speak of 
these sciences separately, for it is clearly impossible without 
a great deal of special knowledge to follow the modern dis- 
coveries in physiology, anatomy, medicine, zoology, botany, 
and geology. 

All these sciences had advanced rapidly since the time 
of Haller and Hunter, Linnaeus and Buffon. Famous 
anatomists and physiologists such as the two Monros, father 
and son, in England, Bichat (1771-1802) in France, 
Camper (1722-1789) and Blumenbach (1752-1840)^ Ger- 
many, had been carrying on the study of the comparative 
structure of men and animals, and training up students to 
understand, far more completely than before, the functions 
of living beings. The followers of Linnaeus, also, all over 
the world had been collecting and sending home for com- 



412 NINETEENTH CENTURY. PT. in. 

parison rare plants and animals formerly unknown, which 
were eagerly studied for the new light they threw upon those 
which had been already dissected and described. 

And so it came to pass .that towards the end of the 
eighteenth century, men became eager not merely to examine 
separate specimens or structures, but to form theories about 
the living beings on the globe. They began to inquire why 
some animals should be so much alike in their general plan, 
and yet so different in their special characters; why the 
same part of the body should be made to serve for different 
purposes in different animals, instead of a special organ being 
provided \ as, for example, the wing of the bat, which answers 
exactly to the front leg of a mouse, but is altered so as to 
be used for flying instead of walking. Then again, as the 
distribution of animals became better known, the question 
arose why certain kinds, such as kangaroos, should be found 
only in Australia, while they are wanting in all other parts 
of the world. Such general questions as these began to 
occupy the minds of naturalists, and we cannot close a 
history of science without trying to understand something 
of the attempts made to answer them. 

Natural System of Plants— Bernard and Antoine de 
Jussieu. — Even while Linnaeus was living, another botanist, 
Bernard de Jussieu (169 9- 1767), had begun to carry out 
his suggestion that plants should be classed by the agreement 
of all their observable characters, and not merely artificially 
by the number of their stamens. But Bernard did not pub- 
lish his catalogue, and it was his nephew Antoine de Jussieu 
(1 748-1836) who first published a book in which the plants 
were arranged according to the Natural System. It was 
Antoine who first sketched out roughly the characters of 
4 Families or Natural Orders ' as we have them now. He 
made 100 families from the plants then known, and though 



ch. xxxviii. METAMORPHOSIS OF PLANTS. 413 

many more have been added since, yet a large number of 
those which he worked out have been permanently adopted. 
The Natural System obliges botanists to take into account 
every part of a plant before placing it into a family or order, 
and as it is often very difficult to determine which are the 
characters of most importance, there is a good deal of 
difference between the arrangements adopted by one botanist 
or by another. But though this is tiresome to pupils, it has 
been very useful in science, for it has served to bring out 
most clearly the way in which plants are related to each other, 
and the fact that in Nature there are not sharp distinctions 
between different kinds of plants, but that a particular species 
may be very closely allied in some of its characters to one 
family and in others to another, so that it is perhaps hardly 
too much to say that our great advance in botany in the 
present century has arisen from two things — (1) from the 
attempt to classify plants according to their natural affinities ; 
and (2) from discoveries made with the microscope, begun, 
as we saw, p. 136, by Grew and Malpighi in the seventeenth 
century, and carried to perfection in our day. 

The great Swiss botanist Auguste Pyrame de Candolle 
(1778-1841) did a great deal to spread the Natural 
System by adopting it in his works, and also by modifying 
it in many ways ; and still further improvements have been 
made by the great Scotch botanist Robert Brown (1773- 
1858), and by Endlicher (1 804-1 849), and Lindley (1799- 
1865). 

Goethe's Theory of the Metamorphosis or Trans- 
formation of Plants, 1790 — We have said that the study 
of the Natural System led botanists to observe more care- 
fully the nature of plants and the manner in which they 
grow. One of the first men who threw any light upon the 
history of the growth of plants was the poet Goethe. Goethe 



414 NINETEENTH CENTURY. PT. III. 

had a deep love of Nature, as may be seen in many of his 
beautiful minor poems, and this love led him in the year 
1780 to devote himself to the study of the anatomy of plants 
and animals. 

When he turned his attention to botany he was very 
much struck with the power which plants have of trans- 
forming or changing the growth of their parts. For example, 
the common wild rose in the hedges has a crown of pink 
petals, with stamens and carpels in the centre ; but the garden 
rose, which is nothing more than the wild rose grown in a 
better soil, has lost the stamens and pistils, or rather has 
changed them into flower-leaves, so that the whole flower is 
one mass of petals, and rarely forms any seeds. 

It is clear, therefore, said Goethe, that the stamens and 
pistil of a plant are nothing more nor less than flower-leaves 
transformed into a peculiar shape, so that they serve to form 
seeds, and to carry on the life of the plant. And this is 
true of all the different parts of the plants. Wherever you 
look in the vegetable kingdom, you will find that every part 
of a plant is nothing more than stem or leaves altered in 
various ways to suit the work they have to do. Thus the 
stem of a geranium, the trunk of a tree, the twining stalk 
of the vine, the straw of wheat, the runners of a straw- 
berry, and the fleshy potato, are all only different forms 
of stems and branches. Again, the two cotyledons of a seed 
which are well seen in the halves of a bean are but the 
first pair of leaves. From between them grows the stem, 
and out of this leaves of different forms, according to the 
peculiar species of plant 

Then, as the plant develops, come the buds of the flower, 
but these again are stems and leaves growing more thickly 
together, but altered and adapted to new functions. We 
find in different plants every variety of flower from mere 



ch. xxxvni. CONRAD SPRENGEL. 415 

green leaf-like blossoms to the most gorgeous colours. The 
green leaves called sepals, which lie under the yellow petals 
in the buttercup, are transformed into brilliantly coloured 
petals in the tulip, while in some cases, such as occasionally 
in white clover, the whole flower, sepals, petals, pistil and 
stamens, has been known to be changed into little leaflets 
growing as if upon a branch. 

For this reason gardeners find it possible to cultivate a 
plant so that it shall be all leaves and no flower, or, on the 
other hand, shall have a gorgeous flower while the leaves 
remain small and insignificant. And thus we are led to see 
that all the different parts of a plant are only peculiar trans- 
formations of simple stems and leaves. 

This beautiful truth of the transformation or metamor- 
phosis of plants we owe to the poet Goethe \ for though 
Linraeus suggested it rather vaguely in some of his writings, 
and a botanist named Wolff seems also to have taught it in 
1766, yet it was Goethe's essay on the ' Metamorphosis of 
Plants,' published in 1790, which first led naturalists to 
consider the question. Goethe's work was very little read 
at first, and he had great difficulty in finding a publisher for 
it, for it was thought that a poet could not know much of 
science ; but Auguste de Candolle seeing what a new light 
Goethe's theory threw upon the study of plants, taught it in 
his works, and then it became gradually known as one of 
the greatest discoveries in modern botany. 

Fertilisation of Plants by Insects— Conrad Sprengel, 
1750-1816. — Another equally important fact was established 
at this time by the German botanist Sprengel, who was the 
first to notice the wonderful connection between plants and 
insects, which Darwin, Hermann Miiller, and others have 
worked out so minutely. 

Christian Conrad Sprengel was Head-Master at Spandau 



4i 6 NINETEENTH CENTURY. pt. in. 

in Brandenburg, but he became so wrapt up in his botanical 
studies that he was obliged to give up his office, and he 
lived in great poverty at Berlin, teaching languages and 
botany. He was so poor that he was not able to publish 
the second volume of his famous work on botany, and the 
publisher had not even given him a copy of the first volume 
for his own use. Sprengel tells us that in the summer of 
1767 he noticed that in the flower of the Geranium sylvati- 
cum the fine little glands containing honey at the base of 
the petals are protected by thick hairs, so that the rain and 
dew cannot reach them, just as our eyes are protected by 
our eyebrows and eyelashes from drops of perspiration creep- 
ing down the face; at the same time he observed that 
insects had no difficulty in passing through the hairs and 
sucking out the honey. 

Again, he found that in the forget-me-not, the line of little 
spots in the corolla points directly to the place where the 
insects must go to get the nectar at the base of the flower. 
This proved, he thought, that there are special provisions in 
flowers to keep the honey for the insects, and to guide them 
to it. So far the flower was of use to the insect ; the next 
point he discovered was that the insect in its turn benefits 
the flower. He observed that the Willow Epilobium, or 
Rose-bay, though it has its stamens and its seed-vessel both 
in one flower, cannot use the pollen from the stamens to 
fertilise the ovules in the seed-vessel, because the stamens 
have withered away and their pollen is gone, before the 
stigma or top of the seed-vessel is sticky and ready to 
receive it. How then do the seeds become fertilised? 
Sprengel watched carefully, and found that insects, in flying 
from flower to flower, brought the pollen-dust clinging to 
them from younger flowers in which the stamens were just 
ripe, and left it in the older flowers where the stigma was 



ch. xxxviii. ROBERT BROWN. 417 

ready to receive it. He afterwards found that in the cypress- 
spurge exactly the opposite takes place. In this plant the 
stigma is ready first, and the insects bring pollen from older 
flowers, and the seeds form in the young flower before its 
own stamens are ripe. 

From these facts Sprengel came to the conclusion that it \ 
is an advantage to a flower to use other pollen than its own ; 
and that the colours and shape of the flowers, and the honey 
they secrete, are all adapted to attract the visits of insects 
for this purpose. He also pointed out that flowers which 
are not visited by insects are generally very insignificant, but 
that they have large quantities of pollen-dust, so that it may 
be carried by the wind. 

Sprengel looked upon all these adaptations as produced 
at the creation of the plant or insect in order to secure that 
they should be useful to each other. But, as we shall see 
in Chapter XLIL, there is now every reason to believe that 
they have been gradually perfected, by the flower adapting 
itself to the visits of some particular insect which can per- 
form for it the work it needs. 

Structural and Physiological Botany — Robert 
Brown, 1773-1858. — The beautiful study of the relation 
between insects and flowers is more easy to understand, but 
certainly not more important, than the investigations into the 
structure and life of plants which have been carried on in 
the present century. Ever since the time of Malpighi and 
Grew the improvement of microscopes and the examination 
of minute parts of plants had been progressing > and Mirbel 
(1776- 1854) in France, and Moldenhauer (1766-1827) 
in Germany, together with many others, had greatly added 
to our knowledge of the structure of the cells and 
tissues of plants, the growth of stems, and the formation of 
seeds. Grew had already pointed out in 1672 that the outer 



418 NINETEENTH CENTURY. pt. hi. 

coat of seeds has a little hole in it which he thought was for 
the purpose of letting the roots of the young plant grow out ; 
and Mirbel in 1815 showed that when a young ovule, such 
as you will find in the ovary of a flower bud, begins to grow 
it appears first as a little swelling made up of cells called 
the nucleus, growing on a short stalk, and that round this 
usually two coats gradually grow, one outside the other, while 
neither of them close quite round the nucleus but leave the 
opening which Grew had observed, and which had already 
been called the micropyle, " or little gate." It is, how- 
ever, to the Scotch botanist, Robert Brown, that we owe 
the first complete explanation of the use of these different 
parts. 

Robert Brown was the son of a minister at Montrose, 
and his first great step in botany was made 
when he went with Captain Flinders' ex- 
pedition to Australia in 1801, and spent 
five months there, bringing back with him 
4000 new species. He then became con- 
servator to Sir J. Banks' museum ; and after 
the death of that eminent botanist he removed 
with the collection to the British Museum, 
where he received ^350 a year, and a pen- 
sion of ^200 granted by Sir Robert Peel at FlG - 2; 

XT , , ,, , aii 1 -i Seed-vessel of nettle. 

Humboldt s request. A whole volume might 

. s> Stigma; sv, Cover- 

be written of the additions which he made ing of seed-vessel ; o, 

to botanical knowledge, but we must confine JjtlL\^n7wl 

ourselves here to his work on seeds. cropyie ; d, Gram of 

He established beyond a doubt that the P ° 

funide, or little stalk/, Fig. 7 2, by which the ovule is attached 

to the ovary, is the channel through which it takes in its 

nourishment ; and that the micropyle, 7/1, is the place through 

which the pollen tube reaches the young ovule and forms a 




CH. XXXVIII. 



STRUCTURAL BOTANY. 



419 



fertile seed. He pointed out that inside the nucleus of the 
ovule is a bag or embryo-sac, e, which has been formed out of 
one of the cells, and that when the pollen-dust d falls on the 
stigma of the pistil, it sends down a tube which creeps through 
the micropyle, and laying its extremity upon the embryo-sac 
causes the young plant to form in it. He also noticed that 
the root of the plantlet is always turned towards the micro- 
pyle, while the shoot or plumule is turned towards the funicle. 
It is easy to see this shoot by simply removing the brown 
seed-skin of an almond, and splitting it in half. The two 
halves are the two cotyledons or seed-leaves with the little 
bud or plumule lying concealed between them, the thickened 
end of it being the rootlet or radicle. 

Robert Brown showed that we may learn a great deal 




Fig. 73. 

1. Nettle-seed cut in half ; a, albumen in which the cotyledon or single seed leaf is 

imbedded. 

2. Almond-seed cut in half. ]_ These two seeds have no albumen, the cotyledon fills 

3. Hemp-seed cut in half, j the whole of the seed-skin. 

/, Funicle ; h, Hilum, where the seed breaks off from funicle when ripe ; m, 
Micropyle ; r, Radicle, or young root ; p, Plumule, or young leafy shoot. 



about the relationship of plants by studying the way in which 
the embryo is placed. Nos. 1, 2, 3, Fig. 73, give three 
seeds, the nettle-seed, the almond-seed, and the hemp-seed. 
In the nettle-seed the embryo is upright, and the micropyle 



420 NINETEENTH CENTURY. 



is at the opposite end to the hilum, or place where the seed 
breaks off from the funicle. In the almond-seed, on the 
contrary, the embryo is turned upside down, or i?iverted ; 
the micropyle is close to the hilum, while the funicle passes 
right round to the other end, carrying the nourishment, as 
before, opposite to the tip of the plumule. Lastly, the 
embryo in the hemp-seed is neither upright nor inverted, 
but curled round so that the micropyle and the funicle are 
both close together ; and yet the rule is still observed, that 
the root should point to the micropyle and the plumule to 
the funicle. The study of the structure and position of the 
ovule are now of great use in classifying plants. 
* Protoplasm — Hugo von Mohl, 1805-1872. — The 
microscope had now revealed the history of some of the 
most delicate structures of plants, but one question remained 
unanswered, namely, What is the living active matter which 
forms the cells, the tissues, and the fibres ? The answer to 
this question was found in the year 1853 by the German 
botanist, Hugo von Mohl, when he showed that the young 
cells of plants are filled with a thick semi-fluid substance 
full of innumerable white granules and that, as the cell 
expands, these granules flow in streams from the centre to 
the circumference of the cell in never-ceasing activity. 

We find this semi-fluid living matter equally in the 
embryo-sac of the young ovule and in all the cells of a young 
plant ; and from it is formed that inert or dead matter which 
composes the cell wall ; and, because it is the simplest form 
of vitality known to us, and out of it all the life of the plant 
springs, Von Mohl called it Protoplasm, or the first foi'mative 
material. 

Chemists have now shown that this living active pro- 
toplasm is composed chiefly of the four elements — hydrogen, 
oxygen, nitrogen, and carbon, and plants have the power of 



ch. xxxviii. SIR WILLIAM HOOKER. 421 



manufacturing it out of the non-living matter in the air and 
soil in which they grow. What this power is we do not know, 
and though the life in our own bodies and in that of all 
animals is supported by this same kind of living matter we 
cannot manufacture it; we, and all the animals can only 
obtain it by feeding on plants, or on other animals which are 
vegetable-feeders, and which therefore have had their food 
prepared for them. 

Geographical and Economic Botany — Sir W. 
Hooker, 1785-1865. — Thus, by means of microscopic 
botany our knowledge of the life of plants has been increased 
enormously in the present century ; but it would not be fair 
to close this subject without speaking of the equally great 
advances in the study of the distribution of plants over the 
globe, and of their use to man. As far as England is con- 
cerned we owe much on this account to Sir William Hooker 
(1785-186 5), who spent his life and a large part of his 
private fortune in encouraging the collection of plants all 
over the world, and in founding the Museums and Her- 
barium of Kew Gardens. He also exerted his influence 
largely in persuading the Government, both here and in the 
Colonies, to publish the Floras of the different districts, so 
that we now have a fairly accurate account of the plants of 
all the English possessions, and of the special homes or 
habits of different species, and this work has been carried 
on most effectively by his son, the present Sir Joseph 
Hooker. 

Any botanist who now wishes to study the history of 
plants has means placed at his disposal, for which Gesner, 
Grew, Malpighi, and Linnaeus longed in vain, and new 
observations are being added daily which should tempt all 
young minds to learn something of a science at once so 
beautiful and so accessible to every one who cares to turn 



422 NINETEENTH CENTURY. PT. ill. 

his attention to it, moreover, we shall see in Chapter XLI. 
that the theory of evolution, which has been worked out in 
the last half of this century, has given quite a new interest 
to the study of every living thing, so that all these facilities 
ought to lead to a much more general knowledge than exists 
at present, both as to the use of plants in our daily life, and 
of their wonderful beauty. 



Chief Works consulted. — Goethe's ' CEuvres Scientifiques ; ' Faivre ; 
Asa Gray's 'Botany;' 'Sachs Geschichte der Botanik;' Robert Brown's 
Works ; Proc. Linnsean Soc. Obituary of Robert Brown ; Von Mohl 
in Wagner's ' Handworterbuch der Physiologie ;' Huxley's 'Physical 
Basis of Life.' 



ch. xxxviii. HUMBOLDT. 



423 



CHAPTER XXXIX. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Humboldt — Lamarck — Cuvier — Geoffroy St.-Hilaire — Comparative 
Anatomy — Development of Animals — 'Homology' — Cuvier's 
1 Regne Animal ' ; His Restoration of Fossil Animals — Von Baer 
on the study of Embryology. 

Alexander von Humboldt studies the Lines of Equal 
Heat over the Globe— Founds the Study of Physical 
Geography— Writes the 'Cosmos,' 1793-1859. — While 
Goethe was studying plants at Weimar, and learning the 
secrets of Nature in the quiet of his own home, another man 
of whom we must now speak was planning to travel in 
distant countries, and to write a history, as far as he was able, 
of the work which Nature is doing all over the world. 

Alexander von Humboldt, who forms a link between the 
science of the eighteenth and the nineteenth centuries, was 
born at Berlin in 1769, and was educated (together with 
his brother William, the great philosopher and politician) at 
the University of Gottingen. At the age of one-and-twenty 
he went to Freyberg, where he was a pupil of Werner. It 
was at this time, when he was only just of age, that he 
formed the plan in his mind of spending his life in studying 
the works of Nature, and writing a i grand and general view 
of the Universe.' 

The first sketch of his book, which he called ' Cosmos, 
or 'The Universe,' was written in 1793, when he was only' 
twenty-four j and the last sheets were printed in 1859, when 



424 NINETEENTH CENTURY. pt. m. 



he was ninety years of age. In the sixty-six years between 
these two dates he collected and published in popular 
language an immense number of facts about nature in all 
parts of the world. 

His chief voyage was to America in 1799, when he spent 
six years in Mexico, and along the shores of the Orinoco in 
the Andes. Here he began one of his greatest undertakings, 
namely finding out the climate of different parts of the 
world, and tracing out isothermal lines, or lines of equal 
heat over the globe, showing what countries have the same 
average temperature, and explaining why some enjoy an 
almost equable climate all the year round, while others are 
very hot in summer and cold in winter. For example, he 
pointed out that Greenland is much colder than Lapland, 
even in places which are on the same line of latitude, 
because a cold current from the North Pole flows past 
Greenland, while the warm Gulf Stream crosses over from 
the Gulf of Mexico and washes the shores of Lapland. The 
importance of this study of variations of temperature was 
first pointed out by Humboldt, and it should be remembered 
as one of his most original investigations. 

Again, in his long journeys through South America, he 
traced everywhere the different species of plants which 
grew at various heights, even up to 20,000 feet on the slopes 
of the Andes. This led him to try and find the reasons 
why certain plants are only to be found in certain areas, in 
the same way that Buffon had worked out the distribution of 
animals. When he returned to Paris in 1804 he had col- 
lected an immense number of facts as to the heights of 
mountains, the climate of countries, the minerals and metals 
found in them, the active and extinct volcanoes, the nature 
of the rocks and soils, the vegetation and the animals ; and 
with the help of the best scientific men in Paris (each 



ch. xxxix. HUMBOLDT. 425 



undertaking his own special science) he published twenty- 
eight large volumes, which contained the conclusions based 
upon the facts he had learnt in his travels. 

In 1827 he returned to Berlin, and was then invited by 
the Emperor of Russia to go on a journey into the Russian 
provinces of Asia, where he spent nine months making the 
same kind of observations that he had made in America. 
In 1830 he was sent to Paris as Prussian ambassador, and 
it was not till he returned to Berlin some years after, that 
he began to publish the ' Cosmos ' he had been preparing 
for so long. 

In this grand work he gives a complete history of 
astronomy, and all the discoveries in it made in his time; l 
and then taking our own world as part of the universe, ) 
he describes the changes which are going on now, or have 
been going on in past times, on the face of the earth. / 
It is to Humboldt that we owe much which makes geo- ' 
graphy interesting. The study of the surface of the globe, X 
of mountain-chains, table-lands, and rivers, the climates of 
countries, the different winds which blow, and the currents 
which cross the ocean ; the way in which plants and ani- 
mals are distributed over the world ; the different races of 
men, and how they have spread over the globe — all these 
and other facts which make geography something more than 
a mere list of names, Humboldt studied during his various 
journeys, and related them with a freshness which had a 
peculiar charm. 

It was not so much that he advanced any one branch 
of science, as that he led men to look upon the earth and the 
universe as one vast whole, and to find a living interest in 
every part of it. In 1858 the last sheets of the 'Cosmos* 
were put into the publisher's hands, but Humboldt did not 
live to see them finished. He had done his part : the work 



426 NINETEENTH CENTURY. pt. hi. 



he had proposed to himself was completed, and he fell 
peacefully asleep on the 6th of May 1859. 

Lamarck— Cuvier — St.-Hilaire. — When Humboldt 
visited Paris in 1804, there were three men holding pro- 
fessorships in the Museum of Natural History in that city, 
who had afterwards a great influence upon the study of the 
science of living beings. These three men were Lamarck, 
professor of zoology; Geoffroy St.-Hilaire, his fellow-pro- 
fessor ; and Cuvier, assistant - professor of comparative 
anatomy. 

The early part of the nineteenth century was, as you 
will remember, a very troubled time for France. The first 
Napoleon was carrying war and desolation all over Europe, 
and Paris was kept in a constant state of turmoil for many 
years. During all this time it is interesting to see how 
steadily and quietly the three men I have mentioned pur- 
sued their search after knowledge. Geoffroy St.-Hilaire 
twice risked his life in saving friends from the terrors of the 
Revolution; and Cuvier held political appointments both 
under Napoleon and under Louis Philippe ; but in spite of 
these duties and interruptions their scientific work was 
never neglected ; and a great part of the knowledge about 
plants and animals which we now possess was accumulated 
during the troublous times of the French revolutions. 

Jean Baptiste de Monet, Chevalier de Lamarck, the 
elder of these three men, was born in 1744 at Bezantin, in 
Picardy, and a somewhat curious circumstance led him to 
devote his life to science. His father intended him for the 
church, but the lad had a passion for the army, and on his 
father's death, in 1760, set off to Germany, where the French 
were then fighting, and soon distinguished himself as a volun- 
teer. Some time afterwards, however, one of his comrades 
lifted him up by his head in joke, and so strained the glands 



ch. xxxix. CUVIER. 427 

of the neck that after a very severe illness he was obliged to 
give up his profession and become a banker's clerk in Paris. 
He had thus time and opportunity to study natural science, 
for which he had always had a great liking, and in 1778 he 
published a small book on botany. Buffon, who was then 
at the height of his fame, was pleased with this work, and 
procured for Lamarck an appointment in the botanical de- 
partment of the Academie des Sciences. From thence he 
went to the Jardin des Plantes, and eventually became pro- 
fessor of zoology in the Muse'e d'Histoire Naturelle. 

George Leopold Cuvier, afterwards made baron Cuvier by 
Louis XVIIL, was born of Swiss parents at Montbeliard, near 
Besancon, in 1769. He, too, was intended for the church, 
because his parents were not rich and he had an uncle who 
could help him in that profession ; but Prince Charles of 
Wurtemburg having heard of his abilities, sent for him and 
gave him a free education in the Acade'mie Caroline at the 
University of Stuttgard. Here he already began in his spare 
moments to read books of natural history and to make drawings 
of plants and animals. When he left Stuttgard he went as 
tutor in a nobleman's family at Caen, in Normandy, and found 
a new and delightful study in the examination of the marine 
animals on the sea-shore. After living there six years, he 
happened to meet the celebrated Abbe Tessier, who had fled 
from the Revolution in Paris, and through his means the young 
Cuvier was introduced to Geoffroy St.-Hilaire and other 
scientific men in Paris, and became assistant-professor of 
comparative anatomy in the Jardin des Plantes. From this 
post he rose to very great honours both as an administrator 
and man of science, holding the posts of President of the 
Institute, Inspector-General of education, Councillor of the 
Imperial University, and many others of equal importance. 

Geoffroy St.-Hilaire, the third and youngest of the three 
20 



428 NINETEENTH CENTURY. PT. in. 

friends, was born at Etampes in 1772. It is curious that he 
also began his education as a priest, and that all these 
three men should have given up the church for science. 
In St.-Hilaire's case it was a passionate love for zoology 
which led him to persuade his father to let him stop in Paris 
to study at the Jardin des Plantes, where he was soon 
offered a post which gave him an excuse for following his 
own tastes. He afterwards joined Lamarck at the Musee 
d'Histoire Naturelle in 1793; and in 1795 it was chiefly 
through his influence that Cuvier was invited to Paris and 
became their fellow-worker. 

It now remains for us to see what was done by these 
three remarkable men. For three years they all remained 
at work in the museum. Cuvier had found in a lumber-room 
four or five old skeletons collected by Daubenton (see p. 
204), and he determined to make them the beginning of a 
museum of comparative anatomy, which afterwards became 
very famous. St.-Hilaire worked with Cuvier, while Lamarck 
began the study of those animals — such as insects, snails, 
worms, shell-fish, sea-anemones, and sponges — which have 
no backbone, and to which he first gave the name of ' in- 
vertebrate animals.' Lamarck's work on these animals is 
one of the most famous he ever wrote. 

In 1798 Cuvier and St.-Hilaire were both invited by 
Napoleon I. to go with the French army to Egypt and 
study the curiosities of natural history which were to be 
found there. Cuvier declined, but St.-Hilaire went, and 
spent three years examining the embalmed animals of the 
Egyptians. He succeeded in 180 1 in bringing away a 
splendid collection of these and other relics from Alexan- 
dria when the French were forced to give up the town to 
the English. These collections were conveyed safely to the 
Museum in Paris in 1802. 



ch. xxxix. LAMARCK. 429 

Lamarck on the Development of Animals, 1801. — 

Meanwhile Lamarck published in 1801 a little work on the 
' Organisation of Living Bodies,' and in it he first suggested 
that the different species of animals were not created separ- 
ately, but had been gradually altered from a few simple living 
forms, so that, in the course of long ages, there had sprung 
up an immense variety of animals in the world. It must 
be remembered that Lamarck had chiefly studied plants and 
the lower animals. We have seen how Goethe showed that i 
all plants are only altered stems and leaves : and the lower 
animals, such as jelly-fish, snails, and worms, differ much 
less from each other than the higher animals do. There- 
fore Lamarck was very much struck with the difficulty there 
was in settling which were distinct forms or species, and 
which might have come from the same parent, and he con- 
cluded that the only difference was that some had branched 
off from the common stock earlier than others, and so had 
become more unlike — just as brothers and sisters are very 
like each other, while distant cousins are much less liable to 
have the same features and expression. 

The more we know of animals and plants, said Lamarck, 
the more difficult we find it to settle which are related to 
each other and which are not. Linnaeus had long ago 
pointed out that among plants which are well known, such 
as the willows in Europe, the cactuses in South America, 
and the heaths and everlastings at the Cape, there are so 
many kinds differing very little from each other that it is 
impossible to say which ought to be considered as separate 
species and which as the descendants of one kind of plant. 

Moreover, we know how much plants and animals are 
sometimes altered even in a few years. For example, by 
growing in a drier soil or up a high mountain, plants 
become stunted and altered in many ways, while birds when 




43© NINETEENTH CENTURY. ft. in. 

shut up lose the power of using their wings, as has been the 
case with our domestic poultry. Man can make a number 
of different varieties both of plants and animals by merely 
keeping those which have the peculiarities he admires. The 
different kinds of pigeon, for example — the pouters, fan-tails, 
tumblers, and others, which are so unlike each other — are 
said by naturalists to be all descendants of the common 
rock-pigeon ; and all the varieties of rabbit have come from 
one wild species. You cannot find a wild pigeon with a 
fan-tail, or a wild rabbit with lop-ears. 

If man, then, in a few hundred years can make such 
changes, 'is it not possible,' said Lamarck, 'that nature in 
all the long ages during which the world has existed may 
have produced the different kinds of plants and animals by 
gradually enlarging one part and diminishing another to suit 
t^he wants of each ? ' These and many other arguments 
Lamarck brought forward in his work in 1801, and again in 
his 'Philosophic Zoologique' in 1809, to prove that the way 
in which the Creator has formed different plants and animals 
has been by altering them gradually out of simple forms. 

There was, however, one very weak point in all his argu- 
ments ; he did not show sufficiently what should cause living 
beings to go on altering, and becoming more and more dif- 
ferent. For if you turn plants and animals, which man has 
altered, out into the fields again, in a very few generations 
they return very nearly to their old forms ; nor can we see 
any reason why the differences between animals should go 
on increasing unless they were picked out and kept apart, 
as men keep them when they want to get new varieties. 

Lamarck did, indeed, point out that climate and dif- 
ference of food would help to alter the nature of an animal, 
but the chief reason he gave for changes taking place in 
them was that the animal itself might cause the alteration in 



ch. xxxix GEOFFROY ST.-HILAIRE. 431 

its form; as for instance, a giraffe constantly wishing to eat the 
boughs off high trees might stretch his neck, and so by de- 
grees each generation might have longer necks than the last 
one. This reason was so weak and ridiculous that it prevented 
naturalists from paying much attention to Lamarck's theory. 

Geoffroy St.-Hilaire points out that the Parts or 
Organs are the same in all Animals, only Modified to 
suit their Wants. — Geoffroy St.-Hilaire was, however, 
inclined to think that there was some truth in Lamarck's 
theory, although Cuvier was strongly against it. Cuvier, you 
remember, had given his time chiefly to the restoration of 
the skeletons of the higher animals, and he was as much 
struck with the immense difference between them as 
Lamarck had been with the likeness of the lower animals. 
Cuvier thought that each animal was at first created sepa- 
rately, and all its parts were arranged expressly to meet its 
wants. He looked upon the creation of each kind of 
animal as something similar to the making of a machine, 
into which we put a wheel here and a valve there expressly 
to make it do the work required. 

Geoffroy St-Hilaire, on the contrary, insisted that we 
never find any part of an animal which we can say was made 
expressly for it. Whenever we examine it closely enough 
we find it is exactly the same as exists in other beings, only 
its growth is altered so as to make it useful to that particular 
animal. The pouch of the Kangaroo, he said, is only a fold 
of the skin which is looser than in other animals ; the trunk 
of the elephant is a nose which has become extremely long ; 
the hand of a man, the leg of a horse, and the wing of a 
bat, are the same organ and have the same bones, although 
they serve such different purposes. ' Nature,' he said, ' has 
formed all living beings on one plan, essentially the same in 
principle, but varied in a thousand ways in all the minor 



432 NINETEENTH CENTURY. pt. hi. 

parts; all the differences are only a complication and 
modification of the same organs.' 

This similarity of structure, or homology as it is called, 
which runs through all animals, was thus first clearly stated 
by St.-Hilaire, and it has now been most carefully worked 
out and confirmed by our living anatomists. Yet Cuvier op- 
posed it to the last, for his mind was full, as we shall see 
presently, of another idea which is equally true ; namely, how 
perfectly each part of an animal is made to fit all the other 
parts of his body ; and it seemed to him impossible that this 
could be, unless each part was created expressly for the work 
it had to do. 

The discussion between the two friends became so 
animated that all Europe was excited by it. It is said that 
Goethe, then an old man of eighty-one, meeting a friend, 
exclaimed, ' Well, what do you think of this great event ? the 
volcano has burst forth, all is in flames.' His friend thought 
he spoke of the French Revolution of July 1830, which had 
just occurred, and he answered accordingly. ' You do not 
understand me,' said Goethe, ' I speak of the discussion be- 
tween Cuvier and St.-Hilaire : the matter is of the highest 
importance. The method of looking at nature which St.- 
Hilaire has introduced can never now be lost sight of again.' 
And he was right, for the doctrine of homology, as taught 
by St.-Hilaire, is one of the strongest arguments for the 
theory of the development of living beings, now held by all 
the most able naturalists, and of which we shall speak in 
Chapter XLI. 

Cuvier proves that the Parts of an Animal agree so 
exactly that, from seeing one Fragment, the Whole can 
be known.— We have seen that Cuvier did not agree with 
many of the views of Lamarck and St.-Hilaire. We must 
now consider what work he did himself; for though all the 



ch. xxxix. COMPARATIVE ANATOMY. 433 

three friends laboured well, Cuvier accomplished the 
most of all. He had a most remarkable capacity for 
work; we find him at the same time restoring skeletons 
and studying each bone with minute care, lecturing to 
large bodies of students, writing the history of all the 
sciences, and examining fossils from the rocks; besides 
presiding over councils and superintending national educa- 
tion. And whatever he touched was done thoroughly and 
with a master-hand. 

His first great work was to collect all the different facts 
of comparative anatomy established since the time of 
Hunter, and, adding a great mass of his own observations, to 
build them up into one complete science of anatomy. In 
his 'Regne Animal,' published in 181 7, he made a new 
classification of the whole animal kingdom, dividing them 
into four great branches. The vertebrata, or animals with 
back-bones; the mollusca, or soft-bodied animals, such as 
snails ; the articulata, or animals, such as crabs, spiders, bees, 
and ants, whose bodies are composed of movable parts, 
hardest outside, and jointed or articulated together ; and 
the radiata, or animals whose parts are arranged round an 
axis, such as star-fish and polyps. These four branches 
he divided again into classes, orders, families, genera, and 
species, making a much more complete classification than 
Linnaeus had done, because it was founded more upon the 
internal structure of animals. 

In this work he pointed out that the parts of an animal 
are made to fit to each other in such a wonderful manner, 
that if only a few bones are placed in the hands of an ana- 
tomist he ought to be able to tell you exactly what all the 
other bones must be. You will remember that Hunter 
had hinted at this when he showed how the teeth of each \ 
species of animal are fitted to the kind of stomach into 



434 NINETEENTH CENTURY. pt. hi. 

which the food is to pass. But Cuvier proved that this is 
true not only of the teeth but of every bone in the skeleton 
of an animal. 

' Every organised being,' he says, ' forms a whole and 
entire system . . . none of its parts can change without a 
change of the others also. Thus, if the stomach of an 
animal is made so as only to digest fresh flesh, his jaws 
must be formed to devour the prey, his claws to seize and 
tear it, his teeth to divide the flesh, and the whole system of 
his organs of motion to follow and overtake it. Nature 
must even have planted in his brain the necessary instinct to 
hide himself and lay snares for his victim. These are the 
general conditions of a carnivorous life, and all animals who 
are to live this life must fulfil them, otherwise they cannot 
exist. And besides these general conditions there are 
special ones, according to the particular kind of life the 
animal has to live, and each of these require modifications 
in the form of the organs ; so that not only the class, but the 
order, the genus, and even the species of an animal are 
revealed by each part of it.' 

And now you will understand why Cuvier could not 
believe St.-Hilaire's theory that all the parts of one class of 
animals — such as the vertebrate animals, for example — are 
made on one model, and that when some organ has to play 
a different part it is altered, and not created for the purpose. 
Cuvier was strongly impressed with the beautiful agreement 
in every part of each particular animal, which enables it to 
provide for all its wants ; while St.-Hilaire was equally im- 
pressed with the general agreement between the structure of 
all animals in any one great class. Both these views were 
true, but in the state of knowledge at that time it was very 
difficult to reconcile them. You must bear this in mind, 
because it is one of the difficulties upon which light is thrown 



ch. -xxxix. FOSSIL ANIMALS. 435 

by Mr. Darwin's observations, which we shall examine 
by and by. 

Cuvier Studies and Restores the Remains of Fossil 
Animals, 1812. — We have seen that Cuvier's knowledge of 
the agreement between the different parts of an animal was 
so great that from even one bone he could tell what the other 
parts of the body must be. The use which he made of this 
knowledge enabled him to reveal a wonderful history about 
the fossils buried in the crust of our earth. 

When he first came to Paris, and for many years after- 
wards, a number of skeletons and parts of skeletons of ani- 
mals were being dug up round about Paris. These were a 
great puzzle to anatomists, for the bones were many of them 
immensely large, and none of them seemed to agree exactly 
with those of any known animals. Cuvier no sooner heard 
of these fossils than he set to work to study them, making 
use of his great knowledge of anatomy to sort out the con- 
fused mass. His practised eye could detect from among 
a heap of bones those which belonged to each other, and 
out of a mere handful of fragments he could make an 
ideal restoration of the animal from which they must have 
come. It was like the work of an enchanter's wand. 

1 At the voice of comparative anatomy,' he writes, ' each 
bone, each fragment, regained its place. I cannot describe 
the pleasure I felt in finding that, as I discovered one cha- 
racter, all its consequences were gradually brought to light ; 
the feet agreed with the history told by the teeth ; the bones 
of the legs and thighs, and those parts which ought to unite 
them, agreed with each other. In a word, each one of the 
species sprang from its own fragments.' 

And so month after month he worked on, and then to 
the great astonishment of naturalists he told them that 
all these animals were of species which are found nowhere 



436 NINETEENTH CENTURY, tr. in. 

upon the earth riow. They were all extinct animals. The 
greater part belonged to hoofed quadrupeds, something 
like our elephant, rhinoceros, and pig; then there was an 
elegant deer-like animal resembling a gazelle, some birds, 
some fish, and a kind of opossum, but all these were in 
some Way different from any which live now. 

Here was a history so strange that at first no one would 
believe it; for it meant that at the time when the land on which 
Paris now stands Was being laid down by the rivers, there 
must have existed a whole group of animals, all of them 
more Or less different from our present species of animals, 
which had not then begun to exist. It had long been 
known that strange shells were found buried in the earth's 
crust, but then naturalists could never be sure that some 
like them might not be living in other parts of the world 
without our knowing it, and they had always believed 
that at least the larger animals had been created quite 
recently at the same time as man. But here were ani- 
mals which no one had ever seen upon the earth, and 
it was impossible to suppose that fifty different kinds of 
creatures of all sizes, some bigger than an elephant, could be 
roaming about the world unseen by any one. Therefore 
there could be no doubt that long before the time of history 
or tradition strange animals must have lived and died, and 
have been buried in the deposits now forming part of the 
earth's crust. 

And when this was once recognised, and attention was 
called to these buried animals, little by little other forms 
were found in older rocks in different parts of the world, 
which appeared to be less and less like living animals the 
older the rocks were in which they were found. All these 
Cuvier described in his famous work called ' Les Ossemens 
Fossiles,' which he published in 1812, and in which he laid 



ch. xxxix. VON BAER. 437 

before the world a startling history of the long succession of 
different animals which must have lived in past ages upon 
the earth. 

And here we must close this very imperfect sketch of the 
work done by the three French naturalists. You ought 
chiefly to remember about them that Lamarck suggested 
that animals have been developed out of a few simple 
forms ; that St-Hilaire proved that animals of one class are 
formed on the same general plan, similar parts being altered 
to serve different purposes in different animals; and thtat 
Cuvier showed that each part of an animal agrees with the 
rest so perfectly that from a few bones it is possible to tell 
exactly what animals had lived and died in past ages. 

GeorTroy St.-Hilaire outlived both his friends, and died, 
blind and paralysed, in 1840. Lamarck had died in 1829, 
in his eighty-fifth year, having been blind for many years. 
Cuvier died on May 13, 1832. On the Tuesday previous 
he had begun his third course of lectures on Natural Science 
at the College de France, and had promised to give in that 
course his idea of creation, and how the Divine Intelligence 
is to be traced through all the operations of nature ; but the 
promise remained unfulfilled ; that same evening paralysis 
set in, and on the next Sunday he died in his arm-chair as 
if he had fallen asleep. He had begged to be buried 
privately, but that was impossible ; on hearing of his death 
men of science flocked from all parts to do him the last 
honour, and his pupils bore him to the grave. 

Von Baer, the Founder of the Study of Embryology, 
1828. — We must not leave this question of the structure of 
animals without noticing in passing a new and important 
study which began about this time. This was the study of 
embryology, or of animals in the earliest stages of their life, 
as in the case of the chicken before it leaves the egg. You 



438 NINETEENTH CENTURY. PT. III. 

know that if you take a bird's egg when it is newly laid, you 
will see inside it a yellow yolk floating in a white fluid. 
But if you take the egg after the mother-bird has sat upon 
it for some days, the yolk will begin to have the form of a 
bird, and if you were to go on taking an egg every day from 
under a sitting hen each one would be found, when opened, 
to be more like a chicken than the one before it, until the 
last, if you opened it just about the time when it ought to 
be hatched, would be a perfect chicken, only that its feathers 
would not be yet growr^ Now the study of the different 
stages of the development of the chicken in the egg, and of 
all living beings going through the same stages, is called 
Embryology, and has become of immense importance in the 
history of animals. 

You will remember that Harvey, Malpighi, and many 
other physiologists, occupied themselves with this study; 
but no discoveries of very great importance were made in 
it before the time of Karl von Baer, a Russian anatomist, 
who was born in 1792 and died in 1876. Von Baer was 
the pupil of a very famous anatomist, Professor Dollinger, 
and while he was working under him at Wiirzburg he made 
for him a number of observations upon the growth of the 
chicken in the egg, which led him to study the embry- 
ology of animals, and to discover the remarkable law of 
which we must now speak. 

Before Von Baer's time it had always been supposed that 
the many kinds of animals, so different from each other, 
must be quite unlike from the very first moment that they 
began to grow, but Von Baer discovered that this is not so, 
but that the embryos or beginnings of an ox, a bird, a lizard, 
or a fish, are so like each other that they can only be dis- 
tinguished by their size ; and, what is still more remarkable, 
they remain alike till they have been growing for some time. 



ch. xxxix. EMBRYOLOGY. 439 

For example, if you could watch the beginning of these four 
animals, there would be a certain time during which you 
could see no difference in their form. Then after a while 
the fish would start off on a road of its own, but still the 
other three would go on all alike. Then, when they had 
grown a little bigger, the lizard would branch off, and only 
the bird and the ox would continue to have the same form, 
until lastly the bird would take on its own peculiar shape, 
and the ox would go on alone, having passed through the 
same stages as the fish, the reptile, and the bird, before it 
began to shape itself like a mammal. You must notice 
carefully that this does not mean that the beginning of an 
ox is at any time like a full-grown fish, which is a mistake 
that people often make; but only that there is a time 
when the minute embryos of these animals are almost in- 
distinguishable the one from the other. 

You will see, if you consider for a moment, that the dis- 
covery of this curious fact gave naturalists a new and much 
more perfect way of classifying animals; for they could 
actually read the history of an animal by watching it in the 
earlier stages of its growth and seeing at what point it 
branched off and put on special peculiarities of its own ; and 
in some of the lower and more obscure animals several mis- 
takes of classification were corrected by this means. There 
was also another very important question settled by Von 
Baer's law. It proved that St.-Hilaire was certainly right in 
saying that animals are formed on one plan, having special 
parts altered to suit their wants, for here in the embryo those 
parts can be seen actually developing differently in different 
animals out of the same beginnings. The study of embry- 
ology has been carried to great perfection since Von Baer 
published his ' History of the Development of Animals ' in 



\ 



440 NINETEENTH CENTURY. ft. hi. 

1828. Among others, Professor Kitchen Parker, deeply 
impressed with the truth of the evolution of animal life, has 
spent more than thirty years in dissecting the embryos of 
all classes of vertebrate animals. By this means he is 
tracing out the hidden links of structure between widely 
separated orders, and though the many proofs of wide- 
spreading relationship which he detects are far too intricate 
and involved to be shortly explained, yet he is slowly but 
surely demonstrating, from embryos often not half an inch 
long, the stages through which fish and reptile, bird and 
beast, have passed in ancient times to their present widely 
varied forms. Another enthusiastic English embryologist, 
Professor Francis Balfour of Cambridge, died by a fatal 
slip on Mont Blanc in 1882, at the early age of thirty-two. 
He had, however, already founded a school of 'Morphology,' 
which bade fair to be a new starting point in science. His 
untimely death has left to the pupils who adored him 
the sad but grateful task of carrying on the work he 
began so well. Lastly, Professor Weissmann of Freyburg, 
and Mr. Geddes of Edinburgh, have brought forward of 
late years theories which are a great help in forming a con- 
ception of the starting-point of the embryo in plants and 
animals, and the relations between growth, reproduction, 
and heredity ; but these theories are too new and too 
difficult to discuss here. 



Chief Works consulted. — L. Agassiz's 'Centenary Address on A. 
von Humboldt,' 1869 ; Humboldt's 'Cosmos;' Lamarck's 'Philosophic 
Zoologique ; ' Cuvier's ' Ossemens Fossiles;' Geoffroy St.-Hilaire's 
' Zoologie Generate Suites a Buffon ;' 'Vie et Travaux de G. St.-Hilaire;' 
Flourens' ' Eloge de Cuvier ; ' Lauder's ' Memoir of Cuvier ; ' Memoir 
of Lamarck ; ' Huxley on Von Baer — Appendix to Baden Powell's 
'"Unity of Worlds ; ' Haddon, ' Introduction to Embryology ; ' Weiss- 
mann, ' Nature,' vol. xxxvi. 1887. 



GEOLOGY. 



441 



CHAPTER XL. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 

Prejudices which retarded the Study of Geology— Lyell, ' Principles of 
Geology ' — Murchison — Louis Agassiz — Glacial Period — MacEnery 
— Boucher de Perthes — Flint Implements — * Antiquity of Man ' — 
Swiss Lake-dwellings — Study of Petrology. 

In 181 1, when Cuvier published his work on 'Fossil Re- 
mains,' William Smith, who, as you remember (p. 221), first 
studied the rocks of England, had nearly completed his geo- 
logical map, and scientific men were beginning, both in 
England and Germany, to understand something of the dif- 
ferent ages of the formations which have been laid down 
from time to time on the surface of the globe ; yet still they 
were prevented from reading the past history of the world 
rightly, by several false notions which continued to prevail. 
People had so long held the belief that our earth had 
only existed a few thousand years, that when geologists 
began to find great numbers of strange plants and animals 
buried in the earth's crust, immense thicknesses of rock laid 
down by water, and whole mountain-masses which must 
have been poured out by volcanoes, they could not believe 
that this had been done gradually and only in parts of the 
world at a time, as the Nile and the Ganges are now carry- 
ing down earth to the sea, and Vesuvius, Etna, and Hecla 
are pouring out lava a few feet thick every year. They still 
imagined that in past ages there must have been mighty 



442 NINETEENTH CENTURY. PT. III. 

convulsions from time to time, vast floods swallowing up 
plants and animals several times since the world was made, 
violent earthquakes and outbursts from volcanoes shaking 
the whole of Europe, forcing up mountains, and breaking 
open valleys. It seemed to them that in those times when 
the face of the earth was carved out into mountains and 
valleys, tablelands and deserts, and when the rocks were 
broken, tilted up, and bent, things must have been very 
different from what they are now. And so they made im- 
aginary pictures of how Nature had worked, instead of 
reasoning from what they could see happening around them. 

Sir Charles Lyell teaches that the Rocks of our 
Earth have been formed by Natural Causes, such as 
are still going on, 1830. — The man who first broke through 
these prejudices was our great geologist, Sir Charles Lyell. 
Charles Lyell was born in Forfarshire in 1797, the same 
year that Hutton died. From his earliest childhood he had 
a great love of Natural History and Science, but as his father 
wished him to become a barrister, he went to Oxford to 
follow the usual course. There he attended the lectures of 
Dr. Buckland, the great geologist of that day, and this de- 
cided him to devote his life to the study of geology. He 
began first by examining the formations round about his 
own home in Forfarshire, and he soon became convinced, 
as Hutton had been before him (see p. 2 1 8), that we can 
only learn the past history of the earth by observing the 
causes now at work. 

What Hutton had suggested Lyell worked out. He col- 
lected with great care all that is known of changes going on 
now all over the world, and the causes which produce them. 
Among these were — • 

istly. The fall of rain, and how it wears away the earth 
and carries it off in little rills to the river. 



ch. xl. SIX CHARLES LYELL. 443 

2dly. The amount of mud carried by mighty streams, 
such as the Ganges, the Nile, and the Mississippi, and laid 
down in the sea at their mouths. 

3dly. The amount of lime, iron, and other minerals 
brought up by springs from the inside of the earth, and thrown 
down on the surface. 

4thly. The tides and currents of the sea, and how they 
wash up fresh land on some coasts and eat away the land 
on others. 

5 thly. The growth of corals in the sea, and how remains 
of their skeletons become cemented into limestone. 

6 thly. The volcanoes which are throwing out lava, and 
how much they have thrown out in historical times. 

7 thly. The different earthquakes which man has wit- 
nessed, how they have broken and dislocated the land, rais- 
ing it in some places, as in New Zealand, and causing it to 
sink in others, as at New Madrid, in America. 

8 thly. The way in which plants and animals are buried 
in the mud of lakes, or at the mouths of rivers, or in peat and 
sand. 

All these and many other changes which are taking place 
all over the world in the present day, Lyell studied with great 
accuracy, and then began to accumulate all this evidence 
in a work showing that what we find in the rocks might 
all have been produced by such causes as these, without 
imagining any extraordinary violence of nature. 

While writing this book he went with another celebrated 
geologist, Murchison, to Italy and Sicily, and there he 
studied not only the rocks which the volcanoes of Vesuvius 
and Etna have been building up for ages, but also saw 
at Syracuse and other places enormous beds of limestone 
filled with shells of kinds which may still be found living. 
The immense thickness of these limestone beds, amounting 



444 NINETEENTH CENTURY. pt. hi. 

in some places to 700 and 800 feet, astonished him greatly. 
He knew they must all have been formed slowly beneath 
the sea, out of the remains of corals and other animals, 
^hose skeletons or shells are composed of lime, and that 
they must afterwards have been raised up to the height of 
3000 feet above the sea, at which he found them; and 
when he thought of the time which this must have taken, 
and remembered that it had all happened since the other 
great masses of rocks below, containing extinct shells, had 
been formed, he felt more than ever convinced that the 
world must be very old to have allowed time for all the 
wonderful changes that have taken place. 

In 1830 his book was published, and though it met with 
great opposition because men's minds were prejudiced the 
other way, yet his facts could not be denied. He showed, 
for example, on the one hand that the river Ganges in India 
carries down every year, and deposits in the sea, as much 
mud as would make sixty of the great pyramids of Egypt, 
and which if it was brought in ships would require 2000 
full-sized merchant vessels laden with mud to sail down the 
Ganges every day. Here, then, was an example of rocks 
being now laid down in the sea, not by violent floods and 
sudden catastrophes, but so quietly that no one even notices 
that nature is at work. 

Then, on the other hand, he pointed out how in our 
own little island, on the coasts of Yorkshire and Norfolk, 
the sea eats away the cliffs, so that towns such as Auburn, 
Hartburn, and Hyde in Yorkshire, which are marked upon 
old maps, have been entirely washed away, and the ground 
on which they stood has been spread out on the bottom of 
the ocean ; and yet this is done so gradually, year by year, 
that new towns of the same name are built up farther inland, 
and no one disturbs themselves about the loss. 



ch. XL. PRINCIPLES OF GEOLOGY. 445 

Then to account for the huge masses of basalt and lava 
which are found in the earth's crust, he reminded his 
readers of the great eruption of the volcano called Skaptar 
Jokul in Iceland, which took place in 1783. In this erup- 
tion the torrent of lava was ninety miles in length, from 
seven to fifteen miles in breadth, and in some places 600 
feet deep, and the whole mass poured out would have made 
a mountain as big as Mont Blanc. 

He then went on to give accounts of the remarkable 
earthquakes which have taken place in times of history : 
the earthquakes in India, in Java, and especially in Cala- 
bria, in 1783, when new lakes were formed by the sinking 
in of the ground, and the rivers were made to run in new 
channels. He showed also how the height of land is some- 
times changed in volcanic countries ; as on the coast of 
Italy, near Naples, where the ground on which the famous 
Temple of Serapis stands can be proved to have been 
raised and depressed twice even in historical times. 

And besides all these obvious changes which men cannot 
help noticing, he proved that other quiet and unnoticed 
risings and fallings of land are taking place ; as, for 
example, in Norway and Sweden, where the land is rising 
out of the sea in some places at the rate of about two or 
three feet in a century ; and in Greenland, where it is sink- 
ing, so that huts built near the shore have to be moved 
inland, because they are becoming submerged in the sea. 

These are a very few of the facts which you can under- . 
stand, by which Lyell demonstrated that the surface of our \ 
earth is always undergoing changes in our own day, and that 
by similar changes going on in past times the whole of the 
crust of our earth may have been built up and carved out. 
In addition to this he showed how plants and animals are 
now being buried in mud and earth, and how their remains 



446 NINETEENTH CENTURY, pt. hi. 

are washed into caves, or preserved in peat-rnosses ; thus 
affording us examples of the way in which the remains of 
ancient animals have become entombed in the earth's crust. 
Thus Sir Charles Lyell taught men to read the true his- 
tory of the earth. It is difficult in the present' day to under- 
stand rightly how great a work he accomplished, for though 
his ideas were ridiculed in the beginning, yet he lived long 
enough to see all men agree with him, and his doctrines 
received as evident truths. Like all other great men, he 
was humble and reverent in his study of nature. His 
one great desire was to arrive at truth, and by his con- 
scientious and dispassionate writings he did much to per- 
suade people to study geology calmly and wisely, instead 
of mixing it up with angry disputes, like those which, in 
the time of Galileo, disfigured astronomy. He travelled 
a great deal, especially in America, and worked out a great 
many facts in geology. But in future ages his name will 
stand out among those of other geologists chiefly as having 
shown that the changes i7i tlie crust of our earth have been 
brought about in tlie course of long ages by causes like tJwse 
thick are still in action. 

After the year 1830, when his 'Principles of Geology' 
was first published, the study of this science went on very 
rapidly indeed. A few years before, Sir Roderick Murchison 
(1792-187 1) and Professor Sedgwick (1787-1873) had begun 
to map out the early formations in Wales with the same 
accuracy that William Smith had employed in England, and 
from this time Murchison continued for many years to un- 
fold the history of the Silurian rocks in Wales and England, 
the Permian rocks in Russia and the ' Fundamental gneiss ' 
or earliest known rocks in Scotland. On the Continent also 
and in America, surveys began to be established to map out 
the ground and ascertain the position and age of the various 



ch. XL. LOUIS AGASSIZ. 447 

formations. As with all the other sciences of the nine- 
teenth century, you must read the details of these advances 
in geology in special works; but there are two great dis-', 
coveries which we must mention very shortly here. These 
are — ist. The fact that much of temperate Europe, Asia, 
and America was at one time covered with ice, as Greenland 
is now; and 2d, that man has lived upon the earth much 
longer than was once supposed. 

Louis Agassiz, 1807-1874. — The man whose name will 
always be remembered as having first traced out the wonder- 
ful history of the great ice-period is Agassiz, the famous 
Swiss naturalist, who was born in 1807 at Mottier, near 
Neuchatel, and died in 1874 in America. 

Louis Agassiz was the son of a Swiss pastor, and he 
forms one among many bright examples in the history of 
science, of men who cared neither for wealth, advance- 
ment, nor ease, but for the study of nature alone, and the 
grand truths to be obtained by it. After receiving a good 
education in the Swiss and German Universities, living 
frugally and economically, as students can on the Continent, 
he took his degree of Doctor of Medicine at Munich in 
1829, having already written several important papers on 
zoology. In 1832 he was made Professor of Natural His- 
tory at the University of Neuchatel; and in 1833 ne Po- 
lished his work on ' Fossil Fishes,' the expenses of the book 
being liberally paid by Humboldt. In 1839 he published 
his grand work on the ' Fresh-Water Fishes of Europe,' 
which cost him so much that he was very poor for years 
afterwards. 

There are very touching passages in some of Agassiz's 
private letters at this early period, when he had a hard 
struggle with life. His enthusiasm breathes out so natu- 
rally, and he speaks so regretfully of want of money, not 



448 NINETEENTH CENTURY. pt. hi. 

for himself, but for the work he longed to complete ; while 
his gratitude is so sensible and heartfelt towards those who 
helped him to bring out his splendid additions to the 
science of zoology. His was a warm-hearted, earnest, and 
active nature, and he was beloved by all who knew him. 
It is pleasant to think that the Americans, among whom he 
spent the latter half of his life, from 1846 to 1874, ap- 
preciated him fully. In 1867, by the kindness of Mr. 
Thayer, he was able to make a most important journey of 
discovery in Brazil ; and up to the last years of his life he 
continued to train up young naturalists to carry on his 
favourite studies. 

Agassiz proves that parts of modern Europe and 
North America must once have been covered with 
Great Fields of Ice, 1840. — It is, however, of the early 
part of Agassiz's life, while he was still in Switzerland, that 
we must now speak. Although his chief study was zoology, 
yet he could not live at Neuchatel, and travel about the 
Alps, without being struck with those mighty rivers of 'ice \ 
called glaciers, which creep slowly down the valley of the 
Alps in Switzerland, carrying with them stones and rubbish. 
(See Fig. 74, p. 449.) 

These glaciers are formed by the snow, which collects 
on the tops of high mountains, and sliding down, becomes 
pressed more and more firmly together as it descends into 
the valleys, until it is moulded into solid ice, creeping 
slowly onwards between the mountains, and carrying with it 
sand, stones, and often huge pieces of rock which fall upon 
it. At last one end of this ice-river reaches a point where 
the air is warm enough to melt it, and here it flows gradually 
away as water, leaving the stones and rubbish it has brought 
down lying in a confused heap, which is called a i7ioraine. 

Towards the end of the eighteenth century a famous 



CH. XL. 



GLACIERS. 



449 



geologist, named De Saussure, spent much time in examining 
the glaciers of the Alps, and pointed out how they are now 
forming large deposits in the valleys out of these heaps of 
rubbish which they bring down from the mountains. Since 
his time many geologists had taken up the study, but it was 




Fig. 74- 

Glacier carrying down Stones and Rubbish (Lyell). 

Professor Agassiz who first spelled out the wonderful history 
we can learn from it, about the former climate of our hemi- 
sphere. He noticed that rocks over which a glacier has 
moved are polished and grooved by the rough stones and 
sand frozen into the bottom of the ice, just in the same way 
as a piece of wood is scraped by the sharp iron at the 
bottom of a plane ; and by these glacial scratches or strice^ 



45° NINETEENTH CENTURY. pt. in. 

as they are called, he could tell where glaciers had been, 
even though there was nothing else to show that ice had 
ever existed in the country. 

Now, when he began to examine the slopes of the Alps 
many hundred feet above the present glaciers, and also in 
places where it is now too hot for ice to remain, he found 
to his surprise numbers of these glacial striae and also 
remains of huge moraines, showing that the glaciers of 
olden time must once have been much larger and have 
stretched farther down the valley than they do now. And 
what was still more strange, these same marks were to be 
seen on the Jura Mountains, on the other side of Switzerland, 
where there are never any glaciers at present ; moreover, on 
the Jura there were found huge blocks, some of them as 
big as cottages, which were not made of the same materials 
as the hills on which they rested, but were broken pieces of 
rock such as are now only found on the Alps. 

It was clear, then, that these enormous pieces of stone 
must have been carried right across Switzerland from the 
Alps near Mont Blanc, and across the lake of Geneva, which 
is iooo feet deep, and then deposited on the Jura range 
near Neuchatel, where one block of Alpine gneiss, called the 
Pierre-a-Bot, as large as a good-sized cottage, sits perched 
on a mountain 600 feet above the top of the lake. How 
had these blocks travelled across the Swiss plains? No 
flood could have carried them, for they were too heavy, and 
besides they were not smooth as stones are which have been 
rolled in water, but were rough with sharp edges. Agassiz 
was convinced, therefore, that they must have been carried 
by ice, and that huge glaciers must once have come down 
from the high Alps right across Switzerland, filling the lake 
of Geneva with ice, and carrying these blocks with them, as 
modern glaciers do now in the Swiss valleys. 



ch. XL. GLACIAL PERIOD. 451 

This was a marvellous history, for it showed that all the 
lower land of Switzerland must once have been buried in 
ice, but other facts afterwards came to light which were more 
wonderful still. In 1840 Professor Agassiz came over to 
visit Great Britain, and when he went to Scotland with Dr. 
Buckland his practised eye discovered at once in the High- 
lands glacial scratchings, remains of moraines, and blocks 
which had been carried by ice ; and soon it became evi- 
dent that these were not confined to Scotland, for Dr. 
Buckland recognised them again in Wales and the North of 
England, where moraines and erratic blocks are to be seen 
in all parts of the country. So that here, too, in our little 
island, there must have been at one time huge glaciers as 
large as those now found in the Alps. 

Nor was this all ; for when once geologists knew where 
to look for these signs of glaciers, it began to be discovered 
little by little that parts of all the northern countries of 
Europe, Norway, Sweden, Russia, Germany, Switzerland, 
Northern Italy, England, and even on the other side of the 
Atlantic, Canada and North America, have been smoothed 
and scratched ; and huge erratic (or wandering) blocks have 
been scattered over them, showing that in very remote ages 
(yet still while very nearly the same kinds of plants and 
animals as now were living upon the globe), the temperate 
parts of our northern hemisphere must have been intensely 
cold, causing a large part of these countries to be covered 
with great fields of ice, as Greenland is in the present day. 
And just as we see now that icebergs break off from the 
Greenland glaciers, carrying with them stones and mud, and 
dropping them at the bottom of the sea ; so in those times 
icebergs floated over many of the valleys of Europe, which 
were then submerged beneath the ocean. You may see in 
the railway-cuttings of Wales, and in the sea-cliffs in the 
21 



452 NINETEENTH CENTURY. rr. in. 

coast of Yorkshire and Norfolk, huge masses of glacial drift \ 
as it is called, made of mud and stones confusedly mixed 
together, which were dropped from icebergs travelling south- 
wards from the ice-fields. 

This period of cold is called by geologists the ' Glacial 
Period ; ' and when you read works on geology you will see 
that it explains in a wonderful manner many curious facts 
in the later history of our earth, and the distribution of 
plants and animals upon it. For the present it is enough 
"N for you to remember that Agassiz first pointed out the signs 
\ of this cold period, and that this discovery was one of the 
earliest rewards of a patient study of causes which are going 
on now; for it is from the ice-action in Switzerland and 
Greenland in the present day that we are able to under- 
stand how these huge ice-fields carried down erratic blocks 
and the mud of moraines during the Glacial Period. 

Geological Proofs that Man lived upon the Earth 
in Ages long gone by, with Animals which are now 
extinct, 1847. — The second remarkable discovery which 
has been made in geology in this century is that of the 
antiquity of man ; or the fact that man must have existed 
upon our earth long before the very earliest times of history 
or tradition, in an age when an elephant and a hyaena, of 
extinct species, roamed about England and France, together 
with some other strange animals which are not now to be 
found upon the globe. 

This discovery, which was not believed for a long time, 
was first announced by a French geologist, M. Boucher de 
Perthes, in the year 1847. It happened that near this 
gentleman's house, at Abbeville in Picardy, gravel-pits had 
been dug from time to time for repairing the fortifications 
of the town, or mending the roads. During these excava- 
tions, in* the beginning of the century, a great many bones 



ch. xl. BOUCHER DE PERTHES, 453 

of animals had been dug up and sent to Cuvier at Paris ; 
and he stated that some of them belonged to animals 
slightly different from any now living, though not so ancient 
as those which came from under Paris (see p. 420). This 
showed that these beds of gravel must have been formed 
long before the times of history or the earliest ages in which 
man was supposed to have been upon the earth. People, 
therefore, were much astonished when M. Boucher de 
Perthes stated in 1847 that he had found very rough stone 
weapons in these beds, such as savages might use, seeming 
to prove that men must have been living at the same time 
as these extinct animals. 

This seemed so incredible that scientific men would not 
even listen to Boucher de Perthes' arguments in his work ^> 
called ' Antiquites Celtiques,' and it was not till 1858, when ^J 
one of our best living geologists, Mr. Prestwich, went to 
Abbeville and took a well-shaped flint hatchet out of the 
undisturbed gravel with his own hands, that people began 
to think that human beings must have been living in the 
world much longer than had hitherto been believed. When, 
however, this was once acknowledged to be true, several 
new facts sprang up to confirm the theory. Many years 
before, in 1825, a Roman Catholic priest, the Rev. J. Mac- 
Enery, had found flint tools, with the bones of the extinct 
elephant, hyaena, and bear, in a cave called Kent's Hole, 
near Torquay, but \ery little notice had been taken of this 
discovery. Now, however, they were thoroughly studied, 
and they showed clearly that men who made rough flint 
tools (such as are still made by savages in many parts of the 
world) must have lived in England, together with a bear, 
an elephant, a lion, and a hyaena, all of species which have 
now ceased to exist. 

Discovery of the Swiss -Lake dwellings, 1853.— 



454 NINETEENTH CENTURY. pt. hi. 

Again, in Switzerland, most curious discoveries have been 
made, giving us proofs of three distinct periods in the life of 
mankind. In the year 1853, when the Swiss lakes were 
very low in consequence of a long drought, wooden piles 
were observed to rise above the water; and when these were 
examined by the Swiss antiquarians, it was found that they 
were foundations of wooden villages, which had been built 
by the inhabitants of Switzerland in past ages. They stood 
some way out in the lake, and must have been joined to 
the shore by wooden bridges which the villagers could lift 
up when enemies came to attack them, and thus become 
protected by the water surrounding them. Habitations of 
this kind are built in the present day by the natives of Papua 
or New Guinea. 

Down below the piles in the mud of the Swiss lakes a 
great number of tools, cooking utensils, bones of animals, and 
even burnt bread and corn, were found ; and the remarkable 
thing was, that the different kinds of tools showed that the 
villages did not all belong to one age. In a few, on the 
lakes of Bienne and Neuchatel, iro?i tools were buried, show- 
ing that when these villages were inhabited men knew how 
to melt iron out of the rocks and make it into tools. These 
villages must have been about the time of the Romans. 

In others, however, only bronze tools were found, and 
these were much older, because bronze was used long before 
iron was discovered. And lastly in some, tools of stone 
only have been found, some beautifully polished, but others 
rough and rude, showing that the men who used them must 
have been mere savages like the Australians now; and yet 
the oldest of these lake-villages have no bones of extinct 
animals in them, and therefore cannot be so ancient as those 
men whose tools were found in the cavern at Torquay and 
the sandpits of Abbeville, or as have since been found in 



ch. XL. PETROLOGY. 455 

England, Denmark, Germany, America, and indeed in almost 
all countries. 

It is impossible, without a knowledge of geology, to 
realise how very long ago these last-mentioned men must 
have lived. For a long time we had only their tools, or a 
few doubtful skulls and bones to prove their existence, but 
in 1886 two human skeletons which were found in a cave 
in the province of Namur in Belgium, together with ex- 
tinct animals, have taught us more about them. These 
skeletons represent thick-set clumsy men of a very low type, 
agreeing well with the other parts of skeletons which 
had been previously found. Their tools were rough and 
unpolished, and the bones of the mammoth, rhinoceros, 
cave-bear, and cave-hyena, lie buried with them. Since 
these men lived and their remains were buried in the rocks, 
there has been time for beds of immense thickness to be 
laid down little by little, as the Ganges is laying them down 
now; for parts of the French valleys to be gradually washed 
away, and their shape altered ; for rivers to change their 
courses, and vast beds of peat to grow over the bottoms of 
the valleys ; and, more than all, for whole races of animals 
which once lived to have died quite away from the face of 
the earth. These facts give some idea of the long ages 
that man must have been upon our globe. 

Study of Petrology. — For nearly a hundred years after 
the time of Werner (p. 216) geologists were chiefly occupied 
in studying the causes of change in the earth's surface, and 
in its inhabitants, and the chronology of the different strata 
as shown by fossil animals and plants. During this time, 
though mineralogy was always taught, it did not form a 
leading feature in geology as in the time of Werner. Of 
late years, however, this has been altered. In 1827 
William Nichol of Edinburgh discovered a method by 



456 NINETEENTH CENTURY. PT. in. 

which transparent sections of rock can be examined under 
the microscope, and this, together with the great advance 
in our knowledge of crystals and their growth, has brought 
back the study of the mineralogical history of geological 
formations. Petrologists, or students of rock-masses, are 
now often able to determine not only the species of 
minerals contained in any given rock, but also the changes 
which these minerals have undergone since they were first 
formed. This naturally is a great help in studying the 
history of a formation, especially in cases of igneous 
rocks ; and while it enables geologists on the one hand to 
distinguish fresh volcanic products from those which have 
since undergone great pressure, it assists them also in 
explaining the nature of the more strictly metamorphic 
rocks, such as schists and gneiss, about which there has 
been so much dispute. 'Petrology' has, in fact, become 
almost a science of its own, which, together with 
1 Palaeontology,' or the study of fossil animals, may in time 
enable us to read with comparative certainty the history of 
the chief formations of the globe. 



Chief Works consulted. — Lyell's 'Principles of Geology,' 'Elements 
of Geology,' ' Antiquity of Man ; ' Lubbock's ' Prehistoric Times ; ' 
' Quarterly Geological Journal,' vol. xxx. : Obituary of Agassiz ; Judd, 
Ann. Address to Geol. Soc 1887. 



ch. xli. BIOLOGY, 457 



CHAPTER XLI. 

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED) 

Facts which led Naturalists to believe that the Different Kinds of 
Animals are descended from Common Ancestors — Darwin — Wallace 
— Theory of Natural Selection — Selection of Animals by Men — 
Selection by Natural Causes — Difficulties in Natural History which 
are explained by this Theory — Foolish Prejudices against it — Present 
state of Biological Science — Carnivorous Plants — Fertilisation of 
Plants — Weissman on Germ-plasma — New Zoological Classifica- 
tions — Discoveries of Fossil Animals — Links in the Animal Series — 
Concluding Remarks. 

Facts which have led Naturalists to believe that 
the different kinds of Animals are descended from 
common Ancestors. — We now come to the first attempt 
of any value which has ever been made, to explain how the 
different kinds of animals and plants have been produced. 
This question is so very difficult, and seems so much 
beyond our grasp, that we find very few people throughout 
the history of science who even tried to answer it. Aris- 
totle, it is true, remarked that we can trace such a close 
resemblance between the different species, from the lowest 
plant up to the highest animal, as would seem to show they 
are related to each other (p. 16). Bonnet, too, thought 
that animals were developed from lower into higher forms 
(p. 202); and Lamarck, as we have seen, boldly suggested 
the same explanation (p. 429). 

But people in general treated these as mere wild specu- 
lations, and were content to say that God had created 
animals just in the same way as they said that the stars 



458 NINETEENTH CENTURY. pt. hi. 

were created by Him, without pausing to consider how He 
has created them. 

Since the time of BurTon and Linnseus, however, many 
new facts had gradually been brought to light about living 
animals ; and fossil species had been dug out of the earth, 
showing that many different forms had lived upon our globe, 
one after the other ; and these new discoveries led naturalists 
to speculate whether some clue might not be found to 
explain this long succession of living beings. 

Then again, as naturalists spread all over the world and 
many new forms of animals and plants became known, it 
was found to be more and more difficult to separate the 
different species and to say which are and which are not 
descendants of one parent. Linnaeus, as we have seen 
(p. 208), pointed this out in the case of plants, and wild 
roses are a very good example of it ; for the different kinds 
run so much into each other, that while one of our best 
botanists has divided them into seventeen species, another 
thinks that many of these must have come from the same 
parent, and that only five species can be distinguished. 
Again, among insects, the well-known naturalist, Mr. Bates, 
has shown us that on the Amazons in South America it is 
often impossible to tell, among some families of butterflies, 
which are the same species and which keep apart from 
each other. Facts like these, of the relationship of living 
beings, had long been forcing themselves upon naturalists, 
and this was one of the reasons given by Lamarck for 
supposing animals to be all descended from a few simple 
forms. 

Another reason was that curious agreement in the 
bones of different animals which had become more and 
more noticed ever since the time of John Hunter, and which 
Geoffroy St.-Hilaire insisted upon so strongly. Why should 



ch. xli. DESCENT OF ANIMALS. 459 

the animals of one class (such as the vertebrate or back- 
boned class) be formed all on one plan even to the most 
minute bones ; so that the wing of a bat, the front leg of a 
horse, the hand of a man, and the paddle of a porpoise, 
are all made of the same bones, which have either grown 
together, or lengthened and spread apart, according to the 
purpose they serve ? And, more curious still, why should 
some animals have parts which are of no use to them, but 
only seem to be there because other animals of the same 
class also have them. Thus the whale has teeth like the 
other mammalia, but they never pierce through the gum ; 
and the boa-constrictor has the beginnings of hind legs 
hidden under its skin, though they never grow out. Here 
again it seemed extraordinary, if a boa-constrictor and a 
whale were created separately, that they should be made 
with organs which are quite useless ; while, on the other 
hand, if they were descended from the same ancestor as 
other reptiles and mammalia who have teeth and hind legs, 
they might be supposed to have inherited these organs; 
just as, for example, a child sometimes has a mole or other 
mark upon its body in exactly the same place as its great 
grandfather had before it. 

Another still more remarkable fact was that pointed out 
by Von Baer, that the embryos of higher animals, such as 
quadrupeds, before they are perfectly formed, cannot be 
distinguished from the embryos of other and lower animals, 
such as fish and reptiles. If animals were created separ- 
ately, why should a dog begin like a fish, a lizard, and a 
bird, and have at first parts which it loses as it grows into 
its own peculiar form ? 

These were facts entirely belonging to living creatures, 
but now others sprang up about fossil species which were 
equally puzzling. We know that certain animals are 



460 NINETEENTH CENTURY. PT. III. 

only found in particular countries ; kangaroos and pouched 
animals, for example, in Australia; and sloths and arma- 
dillos in South America. Now it is remarkable that all the 
fossil quadrupeds in Australia are also pouched animals, 
though they are of different kinds and larger in size than 
those now living ; and in the same way different species of 
sloths and armadillos are found fossil in South America; 
while in the rocks of Europe fossil mammalia are found, 
only slightly different in form from those which are living 
there now. Naturalists therefore asked themselves again 
— ' Would it not seem likely that the living pouched animals 
of Australia, and the sloths and armadillos of America are 
the descendants of the dead ones in the rocks, although 
they have in the course of long ages become rather different 
from them; while oxen, bears, wolves, etc., are also the 
descendants of those which are found buried in the rocks 
of Europe ?' 

Gradual Succession of Animals which have ap- 
peared, upon the Globe. — This seemed still more likely 
as the study of geology advanced, and it became clear that 
a gradual succession of higher and higher animals had 
appeared upon the globe. Thus, in the oldest rocks con- 
taining fossils, we find no monkeys, no quadrupeds, no rep- 
tiles, no amphibians such as our frogs, but only shells of 
marine animals, and a few bones of fishes, of kinds quite 
different from those now living. 

Then in rocks above these we find the fish becoming 
very abundant and varied, and higher still we meet with 
footprints of some animal with feet ; and the bones of an 
amphibian, somewhat like a frog, are next found. In these 
times the fish began to cease to be monarchs of the water, 
for a little higher up huge swimming reptiles, like our 



ch. xli. SUCCESSION OF ANIMALS. 461 

crocodiles and lizards, but much larger, have left their 
bones in the rocks. Next come reptiles with wings, which 
measure sixteen feet across from tip to tip, and we must 
picture these huge flying lizards, with wings like bats, roam- 
ing over the globe with no higher animals to persecute 
them. 

But they were only to have their turn, for in rocks formed 
a little later there appear two skeletons, one of a small 
creature half reptile half bird, about the size of a pigeon, and 
the other of a real bird with some of its feathers still remain- 
ing ; and in beds of about the same age there occurs the 
jaw of a small insect-eating animal something like an ant- 
eater. Birds and quadrupeds therefore had now begun to 
exist, and soon the bones of pouched animals are found, and 
then of mammalia, like our moles and shrews ; and from 
this time the reptiles become smaller, as if they were kept 
down and gradually destroyed by the higher animals, and the 
quadrupeds become larger and more powerful ; till, in those 
beds which Cuvier studied near Paris, we find the gigantic 
elephant and rhinoceros-like animals we spoke of before ; 
while in beds of about the same age occur the first bones of 
monkeys. 

This is a very rough sketch of the order in which ani- 
mals are found in the earth's crust. The lower kinds first, 
and then gradually higher and higher forms as they come 
near to our own time ; and if we could study them more 
closely you would see that in rocks nearly of the same age 
the forms are always very like each other, while the farther 
apart the formations are, the more different are the animals. 
It is true that there are very few close links to be found 
between fossil animals ; but when we remember that nearly 
all the rocks in the earth's crust are made out of others which 
have been destroyed, it is scarcely wonderful that so few 



+62 NINETEENTH CENTURY. pt. hi 

skeletons should be found of those that were once buried, 
and it is not likely that many of these would be just the in- 
termediate forms we want. Still some have come to light, 
for a bird-reptile has been found in the rocks of Kansas, in 
America, which has a skeleton like a bird, but teeth and jaws 
like a reptile ; and a reptile has been dug out of the Stones- 
field slate in England, which Mr. Huxley says must have 
hopped like a bird, having legs, neck, and a bird-like head, 
while it had, nevertheless, teeth like a reptile. Again, horses 
have been found in the rocks of America which have sepa- 
rate toes, and others in which the toes are beginning to 
grow together, showing how they may have been gradually 
altered into our one-toed horse. 

And here again, those who studied fossil animals asked 
why these forms should succeed each other, gradually pass- 
ing on into the living forms of our own day, which are all 
slightly altered copies of these fossils of the rocks ? 

How can Plants and Animals have become altered ? 
— It was questions such as these which seemed to call for 
answers, and to find none except the one proposed by 
Lamarck ; namely, that the different kinds of animals are 
all descended from a few simple forms. If this were so, then 
it would be quite natural that higher and higher forms should 
appear gradually upon the earth, and that the kinds most 
alike should follow directly upon each other, those which are 
now living being very like their ancestors in the newest 
formation in the earth's crust. It would also help us to 
understand why animals of the same class should have the 
same bones, and why some should have parts remaining in 
their body which are no longer of any use ; and lastly, it 
would explain why naturalists have so much difficulty in 
distinguishing nearly related species. 

But though these reasons made it seem very likely that 



ch. xli. DARWIN'S THEORY. 463 

all animals are only different branches from one stem, yet 
this could only be a mere speculation, unless some one 
could point out what has made them differ so much from 
each other. Lamarck, as we have seen, could not do this, 
and therefore his suggestion was passed by ; and it was not 
till five -and -twenty years ago that two naturalists, Mr. 
Darwin and Mr. Wallace, discovered a law which is cer- 
tainly true in itself, and which accounts for many of the 
facts. Their theory, which we must now consider, was so 
new that it was opposed on all sides, just as the Copernican 
theory was opposed in the sixteenth century, the circulation 
of the blood in the seventeenth century, and the theory of 
combustion, which overturned phlogiston, in the eighteenth 
century. We live in the midst of the discussion about the 
origin of species, yet even within the short space of a 
quarter of a century it has almost outlived opposition, and 
there is scarcely a naturalist of note who does not in one 
form or another accept the Darwinian theory, which we 
must now try to understand. 

Theory that Natural Selection has caused the 
various kinds of Plants and Animals to differ per- 
manently from each other,— Darwin, 1809-1882.— 
The Theory of Natural Selection, or the Darwinian theory 
as it is often called, was chiefly worked out by the great 
naturalist Charles Darwin, who was born in 1809 and died 
in 1882. When he was only two -and -twenty, Mr. Darwin 
went in her Majesty's ship ' Beagle ' to survey the coast of 
South America and sail round the globe ; and on his return 
he wrote an account of the geology and natural history of the 
countries he had visited. He tells us himself that even so 
early as this he noticed many facts which seemed to him to 
throw light on the difficult question of the origin of the dif- 
ferent species of plants and animals; and he spent twenty years 



464 NINETEENTH CENTURY. PT. ill. 

carefully collecting in England all the knowledge he could 
upon the subject. But he did not publish it, for he wanted 
more and more evidence ; and as Newton waited sixteen 
years for more convincing proof before he announced his 
theory of gravitation, so Mr. Darwin would have delayed 
much longer than he did if a remarkable circumstance had 
not obliged him to speak. 

It happened that while Mr. Darwin was working in Eng- 
land, another great naturalist, Mr. Alfred R. Wallace, who 
was then in the Malay Archipelago, also thought that he 
had discovered the way in which animals are made to vary 
in the course of long ages. He sent home a paper on the 
subject, and, though he had never heard of Mr. Darwin's 
theory, it was found that he had worked out the same result 
sometimes almost in the same words. 

Sir C. Lyell and Dr. Hooker of Kew were so much 
struck with the fact that these two men had solved the 
problem almost precisely in the same way, that they begged 
Mr. Darwin to allow one of his papers, written many years 
before, to be published with Mr. Wallace's, and the two 
essays were read the same evening, July 1, 1858, at the 
Linnaean Society. A year later, in November 1859, Mr. Dar- 
win's famous work, ' The Origin of Species/ was published. 

* The Theory of Natural Selection,' or the choosing out 
by natural causes of those plants and animals which are 
best fitted to live and multiply, rests upon a few simple facts 
which you can understand. 

Firstly, all living beings multiply so rapidly that there 
would be neither room nor food enough upon the earth for 
them if they were all to live ; therefore immense numbers 
must die young, and those will live the longest and have 
children to follow them who are best fitted for the kind of 
life they have to lead. 



ch.xli. DARWIN'S THEORY. 465 



Secondly, no two living beings are ever exactly alike ; 
but children always inherit some of the characters of their 
parents, so that if any being has a peculiarity which makes 
it better fitted for its life, and consequently lives long and 
has a large family, some of its descendants will most likely 
inherit that peculiarity. 

Now it is not difficult to understand that if useful 
peculiarities of different kinds are handed down in this way 
from parent to child, those who inherit them will in time 
begin to be remarkable for different qualities. For example, 
suppose that in a nest of young birds, one with strong wings 
lives and has young because it can fly far and get food, 
while another also lives and has young because its feathers 
are dark, and the hawks cannot see it in the grass. Then 
those descendants of the strong -winged bird which also 
have strong wings, will be most likely to live on in each 
generation, and will pass on this peculiarity to their children ; 
while the descendants of the dark-coloured bird will also sur- 
vive in each generation exactly in proportion as their plum- 
age is adapted to hide them ; and thus the strong-winged 
birds and the dark-winged birds will in time become very 
different from each other. This is roughly the theory of 
' Natural Selection ;' that nature allows only those animals 
to live which in some way escape the dangers which threaten 
their neighbours, and thus in time the race becomes altered 
to suit the life it has to lead. 

There is only one difficulty. It is clear that the strong- 
winged birds must not pair with the dark-winged birds, or 
otherwise both peculiarities would come out in the young 
birds, and the two kinds would no longer remain distinct. 
And this is the one stumbling-block in the theory; we 
have never yet been able to trace out two varieties of an 
animal which have become so different that they do not pair 

2 H 



466 NINETEENTH CENTURY. PT. iil 

together. You should fix this difficulty firmly in your mind, 
because it is almost the only real one we shall meet with. 
Mr. Darwin's answer to it is, that we have only watched 
plants and animals for such a short time, and even then not 
with this idea in our minds, so that we are not likely to 
have found a case to help us. It has indeed been observed 
that animals, if left free to choose, do often pair with those 
which resemble themselves, and do in some cases show a 
dislike to those that differ ; still this is not proved to be 
always the case, and it must be acknowledged to be a 
difficulty. 

Selection of Animals by Man. — But now setting this 
aside, let us see what proof there is that animals vary, and 
that they can be picked out, so that any peculiarity may be- 
come stronger in each succeeding generation. The best 
instance is in pigeons. All our pigeons come from the 
common wild rock-pigeon ; and the way in which all our 
pouters, fan-tails, barbs, and other pigeons have been pro- 
duced, is by merely picking out from the young ones those 
which had either large crops, or wider tails, or longer beaks, 
and pairing them together, so that the young birds had these 
peculiarities still more strongly. The same thing is true of 
our different kinds of oxen, sheep, horses, and fowls ; so we 
see clearly that different varieties can be produced by choos- 
ing out particular animals. Man does this quickly, because 
he only attends to one peculiarity, which interests him ; but 
nature does it very slowly, because no animal can live unless 
every part of it is fitted for its life better than in those which 
are killed off. , 

Selection by Natural Causes. — Now Mr. Wallace has 
calculated that one pair of birds having four young ones a 
year, would, if all their children, grandchildren, and great- 
grandchildren, lived and were equally prolific, produce about 



ch. xli. NATURAL SELECTION. 467 

two thousand million descendants i7i fifteen years. And Mr. 
Huxley tells us that a single plant producing fifty seeds a 
year would, if unchecked, cover the whole globe in nine years, 
and leave no room for other plants. 

It is clear, therefore, that out of these numbers millions 
must die young, and it is only the most fitted in every way 
that can live and multiply. One example from Mr. Darwin's 
book will show you how complicated the causes are which 
determine what particular kinds shall flourish. He tells us 
that the heartsease and the Dutch clover, two common 
plants, can only form their seeds when the pollen is carried 
from flower to flower by insects. Humble-bees are the only 
insects which visit these flowers, therefore if the humble-bees 
were destroyed in England there would be no heartsease or 
Dutch clover. 

Now the common field-mouse destroys the nests of the 
humble-bee, so that if there are many field-mice the bees 
will be rare, and therefore the heartsease and clover will not 
flourish. But again, near the villages there are very few 
field-mice, and this is because the cats come out into the 
fields and eat them; so that where there are many cats 
there are few mice and many bees, and plenty of heartsease 
and Dutch clover. Where there are few cats, on the con- 
trary, the mice flourish, the bees are destroyed, and the plants 
cease to bear seed and to multiply. And so you see that it 
actually depends upon the number of cats in the neighbour- 
hood how many of these flowers there are growing in our 
fields. 

But now let us suppose for a moment that among the 
field-mice there are some whose skin has a slightly peculiar 
smell, so that the cats do not eat them when they can find 
others. Clearly these mice would live longest and have 
most offspring ; and of these again, those with strong smell- 



468 NINETEENTH CENTURY. FT. hi. 

ing skins would live ; and so after a time a new race of mice 
would arise which would be independent of the cats, and the 
bees would have a poor chance of living, and consequently 
the flowers of bearing seeds. 

But this might in the end give rise to quite a new race 
of plants, for it is believed that some moths would visit the 
clovers, only, as Mr. Darwin points out, they are not heavy 
enough to weigh down the petals of the flowers so as to 
creep inside them. But as no two flowers are ever exactly 
alike, it is very likely that the petals of some blossoms will 
droop a little more than in the others, and so if the bees 
became scarce, these blossoms with drooping petals might 
live on, because the moths could creep into them and carry 
their pollen from flower to flower ; and thus a new race of 
clover with drooping petals might spring up independent of 
the cats, the mice, and the bees, and would become a new 
species. 

You must especially notice in this imaginary example 
that it is only useful variations which can be passed on 
from generation to generation. If the smell of the mice 
(which would probably come from some peculiarity in the 
pores of the skin) did not preserve them from the cats, the 
strong-smelling mice would not live, and a peculiar race 
would not arise ; in the same way, if the drooping leaves of 
the clover did not enable the moths to enter, those plants 
would die out like the others. And this is one of the most 
striking facts which Mr. Darwin has pointed out; namely, 
that no variation will continue and increase from generation 
to generation unless it is useful to the plant or animal which 
possesses it ; so that if this theory be true, every beautiful 
colour which we admire in animals and plants, every minute 
detail in their form and structure, is not only to be admired 
for its beauty, but because it is an evidence of that won- 



ch. xli. NATURAL SELECTION. 4^9 

derful harmony of nature which keeps every part, however 
insignificant, exactly fitted to do its work in the one great 
scheme of creation. 

Difficulties in Natural History explained by 
Natural Selection. — And now, if we adopt Mr. Darwin's 
explanation, you will see how St-Hilaire and Cuvier could 
both be right when the former said that all animals are formed 
on one plan, and the latter, that each part of an animal is 
exactly fitted to work harmoniously with the rest of its body. 
For if animals have been gradually altered the one from the 
other, it is natural they should all be made on one plan ; 
as, for instance, if the ancestor of the bat, millions of years 
ago, was also the ancestor of those animals out of which the 
horse has come, then the bones of the bat's wing may well 
be similar to those of the horse ; while, on the other hand, 
if no variation can become fixed, and develop into import- 
ant parts or organs unless it is useful, it is clear that all the 
parts of an animal must have been gradually modified so as 
to fit each other and to work in the best possible way for 
its well-being. Again, it explains why the living animals in a 
country should be of the same class as those found fossil in 
the earth, though slightly different from them. For if in 
Australia the ancestors were pouched animals, it must take 
a very long time before their descendants could be anything 
else, although they might begin to differ in many points of a 
less fundamental nature. 

Lastly, it enables us to understand why we find the lower 
forms of life in the oldest rocks, and why gradually, as 
animals multiplied and the struggle for life became greater, 
more and more complicated forms should arise, from the 
improvement and inheritance of specially useful parts ; so 
that the higher animals have a greater number of different 
parts to perform different actions, just as a civilised country 



470 NINETEENTH CENTURY. PT. ill. 

with a great number of skilled people in it has men of 
different trades and professions, one to brew and one to 
bake, one to dig the ground, and to grow cotton and flax, 
and another to weave them into garments. 

This will give you a very small glimpse of some of the 
apparent anomalies which are explained by the theory of 
natural selection. The subject is so difficult to understand 
thoroughly, that you must not expect to have more than a 
slight notion of it, and must be content for the present with 
\ knowing that our greatest living naturalists, who have made 
ja careful study of living and fossil animals and plants, all 
\pelieve it to be true. 

And as this is so, it is extremely foolish to be prejudiced 
against it, as some people are, by the idea that animals 
formed in this way can be less God's creation than if they 
were made in any other way. The whole history of science 
teaches us that men, in all ages, have constantly taken false 
alarm when it has been shown that God's ways are not our 
ways, and that the universe is governed by far wider and 
more constant laws than we had imagined in our little 
minds. But in the same way as the planets are none the 
less held in God's hand because we now know that it is by 
the law of gravitation that He governs their movements, so 
every plant and animal must be equally His creation, in 
whatever way they have been developed. Above and be- 
yond all these laws which we can trace there remains ever 
the One Great and Supreme Creator whom Anaxagoras wor- 
shipped instead of the heathen gods of Greece (see p. 14), 
when his fellow-countrymen condemned him as an unbe- 
liever because he believed not in many, but in One God. 
/"-"A humble, earnest spirit seeking knowledge must indeed 
find in modern science a deep revelation of the Unity and 
J., Unchangeableness of the Creator. Instead of many widely 



ch. xli. NATURAL SELECTION. 471 

different sciences standing each alone, which the great men 
of earlier centuries worked out, we are beginning to be able 
to discern one constant power working through them all ; 
while still new fields of discovery, such as that which spec- 
trum analysis has only lately opened out to us, help us to 
bear in mind how little we know, and how much more vast 
than anything that we can imagine must be the great 
scheme of Creation which is being worked out around and 
within us. 

But even if future study should lead biologists to modify 
in some ways Darwin's theory of the origin of species, the 
impulse which it has given to the study of plants and 
animals cannot be over-estimated. Fifty years ago the 
naturalist might, and did, find great interest in discovering 
new species of animals and plants, and studying their habits 
and nature ; while the anatomist and physiologist classified 
forms according to their structure, and thus we were 
beginning to arrive at a fair general view of the plant and 
animal kingdoms. Here, however, the interest ended ; for 
there was then no idea that the structure, nature, and habits 
of living beings could help us to unravel the history of past 
life upon the globe ; nor that every hair, and bone, and tint 
of colour is a clue to the working of general laws by which I 
the various forms have arisen and filled the earth. This 
conception was only possible after Darwin had shown in 
his 'Origin of Species' (see p. 464) that 'the structure of each 
part of each species, for whatever purpose used, will be the 
sum of the many inherited changes through which that 
species has passed during its successive adaptations to 
changed habits and conditions of life.' 

Now, see what a field this opens to the most humble 
student of nature, if he only work conscientiously. For- 
merly, a plant or animal stood alone, and the question, how 



472 NINETEENTH CENTURY. PT. in. 

it came to be what it is and where it is, did not arise. 
But now, taking a plant, for example, we have to learn in 
what it differs from the simplest plants known, and for 
_ what reasons it has gradually acquired the various parts by 
Which it performs its functions. From this point of view, 
its roots and the way they grow, its leaves, the hairs that 
cover them, the chlorophyll which they use to assimilate 
their food, even their movements by night or by day, have 
all a real significance, as Dr. Julius Sachs has so graphic- 
ally described in his works. Again, the study of the 
curious structure of flowers, their manner of forming their 
seeds, and the numerous contrivances for attracting or 
repelling insects, has become a science in itself, enriched by 
the countless observations of Darwin, Hermann Miiller, 
Kerner, Sir John Lubbock, and others. Yet still so much 
remains to be done that any one who will work in the 
field or garden, with the theory of evolution as his guide, 
may add to the links in Nature's chain, by following which 
we are gradually tracing out the past history of plant life. 

In the same way the food of plants, and the manner in 
which many have been driven to procure it, so to speak, 
illegitimately, now offers a new line of research. Parasites, 
epiphytes, saprophytes, all help us to trace out 'adaptations 
to changed conditions of life,' and to learn how a plant 
loses organs, or gains new ones, as it leaves the ordinary 
road of plant life. 

Take, for example, the carnivorous plants, such as the 
Dionsea, the Drosera or sun-dew, and the Pinguicula, which 
actually feed upon the juices of insects and other small 
animals which they enclose in their leaves. As long ago 
as 1768 an English botanist named Ellis pointed out that 
the leaves of the Dionaea close over any unfortunate 
insect which alights upon them, and cover it with a sticky 



ch. xlii. BIOLOGY. 473 

fluid, and Dr. Curtis, in 1834, showed that this fluid acts 
like the gastric juice of an animal in digesting and dissolv- 
ing the animal matter. Since then Mr. Darwin's work on 
'Insectivorous Plants' (1875) and Dr. Burdon Sanderson's 
experiments have dealt with the whole subject It seems 
that even the lightest gnat resting on the glands of the 
leaves of one of these species excites the minute hairs 
with which they are covered and causes the leaf to close, 
and Dr. Sanderson has shown that the same kind of elec- 
trical current is set up in the leaf by this movement, as" 
occurs 'in our own muscles when they contract. The 
glands of the leaf next begin to pour out a sticky fluid, 
which dissolves the substances of the insect in just the 
same proportions and in the same manner as the gastric 
juice of our stomach dissolves the substances in our food ; 
and lastly, when the leaf unfolds, and the tentacles or little 
hairs rise up again, letting the refuse of the dead insect 
drop, the glands cease to give out the fluid until another 
insect is caught and the process begins again. The whole 
history of these carnivorous plants, though they are excep- 
tional in the vegetable kingdom, is one of the most interest- 
ing that can be imagined, and forms another unexpected 
link between the nature of plants and animals, while at the 
same time we have no new organs created, but only modifi- 
cations of those common to plant life. 

Lastly, the mere collector of plants has quite a new 
interest in his work, for it is no longer an ultimate fact that 
any particular plant inhabits such or such a country. We 
have now to learn how it came there, to trace out its near 
relations in other countries, and to track its line of migra- 
tion, just as we do that of a race of people ; explaining the 
modifications it has undergone by the length of time it has 
been living under new conditions, separated perhaps by a 



474 NINETEENTH CENTURY. pt. hi. 

wide or impassable barrier from the home where first it 
arose, and where climate, soil, and the other plants among 
which it had to hold its own, were very different from those 
now surrounding it. 

All these new interests are now within the grasp of the 
student of botany, together with a host of observations 
regarding internal plant-structure, and the nature and con- 
tinuity of the gernvplasma in plants as lately propounded 
by Professor Weissman. In fact, physiological botany has 
become one of the most interesting and suggestive of 
studies, while such men as Bornet, Muret, Schimper, de 
Bary, and others, have now worked out the difficult question 
of the fertilisation of ferns and mosses, in which, neverthe- 
less, we trace the connection of their modes of fructification 
with those of higher plants. 

When again we turn to Zoology we find still more the 
healthy influence of a connected theory of life. For among 
animals there is such an immense variety of forms that the 
gradations of structure from the simplest to the highest, and 
their relations to each other, are a source of never-failing 
interest. Here the investigations of Parker, Balfour, and 
others (see p. 440), come in to help us, by showing the 
resemblance of the embryos of higher forms to the various 
gradations found in lower ones of the same or of nearly 
allied groups ; and structures which were formerly merely 
puzzling anomalies now find their true place as links in 
the tangled web and woof of gradually developing animal 
life. So, too, when we see such different structures as the 
fin of a fish, the wing of a bird, the leg of a horse, and the 
arm and hand of a man, formed all on the same general 
plan, we no longer fall back helplessly on the idea that 
mere poverty of invention caused them to be created on 
the same lines. We have now a sufficient reason for their 



ch. xlii. ZOOLOGY. 475 

likeness in the fact that in ages long gone by they started 
from a common source; and every resemblance we trace, in 
parts now used for different purposes, is only additional 
proof of the marvellous way in which the same structures 
are adapted to changed habits and conditions of life. The 
classifications of animals, as given by Owen and Huxley 
in England, and Von Baer, Gegenbaur, and Haeckel in 
Germany, and in fact by all zoologists of our time, is 
formed upon this conception of the actual relation of living 
forms, and so classification becomes no longer a mere 
arrangement for convenience, but a real statement of what 
we know about the links which bind the animal creation 
together. But in order to find these links an almost in- 
credible amount of patient work must be done. It is not 
enough to understand merely the prominent characters of 
an animal. Its minutest structure must be known, for 
those parts of least importance in its own life are often of 
the greatest value to the naturalist, because they are the 
remains of some organ which was useful to a remote ancestor. 
And when we are once started on this road, the help 
and suggestion which comes in from all sides is endless. 
Mr. Romanes, for example, has found in the Medusae 
or jelly-fish traces of a nervous system, rudiments of eyes, 
and sacs of mineral matter, forming probably a rude hearing- 
apparatus, while on the other hand a rudimentary unpaired J 
eye has been found in Lizards very nearly allied to the eye ' 
of invertebrate animals. Thus we find constantly new links 
between the two divisions of the animal kingdom, and it is 
probable that in time the earliest beginnings of organs 
similar to our own may be traced in extremely simple 
invertebrate animals, and from thence upwards through the 
various branches of the animal kingdom till they reach their ? 
highest development in man. 
22 



476 NINETEENTH CENTURY. pt. in. 

On the other hand, if instead of going down to lower 
living forms we go back into the history of the past, 
PalcBontologv, or the study of fossil animals, first brought 
into prominence by Cuvier in 1812, teaches the same 
lesson. We saw (p. 435) how the discovery of animals 
slightly differing from living ones startled the world at the 
beginning of the century, and since then, year after year 
has been adding to the evidence (p. 462) that life in the 
past helps us to complete the links between different living 
forms. Of late the chief additions to our knowledge have 
been made in America, where Dr. Leidy, Professor Cope, 
and Professor Marsh have brought to light an immense 
number of fossil skeletons. Some of these help us to trace 
the gradual development of animals, as in the case of the 
horse, whose probable ancestors have now been found 
among the fossils of the Rocky Mountains, beginning with 
a little creature about the size of a fox, with real toes 
instead of a hoof; showing that, whereas the horse was 
formerly believed to have been always confined to Europe, 
till it was taken to America by the Spaniards, in real truth 
its ancestors were American, and it must have migrated to 
Europe in past ages. Others, again, are curious animals, 
half reptiles, half birds, and some of these are so enormous 
that it is difficult to imagine how they can have walked as 
they did on their hind feet. The largest of these mon- 
sters, Titanosaurus monianus, found by Professor Marsh 
in Colorado, must have measured from fifty to sixty feet in 
length, and have been at least thirty feet high when it stood 
upright. It lived in the Cretaceous period, or about the 
time when all the chalk of our North and South Downs 
was being formed in the depth of the sea. 

It is easy to see that such discoveries as these make us 
take a much grander view of the history of animals and 



PALjEONTOLOG V. 477 



their relationship than when it was believed that those 
creatures now known to us were all that had existed 
since the creation of the world, while, at the same time, 
they afford the evidence we need as to the lines of migra- 
tion along which related living forms, now widely separated, 
have passed to distant lands. Thus, if it were not that we 
find marsupials in Europe in Triassic times, how could we 
explain the presence of opossums in South America and 
kangaroos in Australia, both of them marsupial forms, yet 
existing at two ends of the world with no links between 
them? So that, here again, as in plants, geographical distri- 
bution has become a grand and interesting problem which 
all naturalists may help to solve, and the theory of the 
relationship and evolution of living forms brings order out 
of confusion. We have only to turn to the grand volumes 
on the different forms of animal life, brought home by the 
'Challenger' expedition in 1876, to see how increasing 
study and discovery lead to ever-widening generalisations, 
uniting the whole of the living kingdom under a system of 
natural and intelligible laws. Is it too much to say that, 
with such a vista before him, and the certainty that any 
observation he may conscientiously make will add to this 
grand conclusion, the young student of Biology has a tempt- 
ing field before him, and a reasonable prospect of doing 
good work if he will only follow carefully in the footsteps of 
such patient investigators as Linnaeus, Cuvier, and Darwin ? 

Concluding Remarks. — This short sketch gives but a 
very imperfect glimpse of the kind of work which is being 
done in science in our own days. The workers are now 
hundreds, where in the seventeenth century they might 
be reckoned by units, and the whole scope of their work 
cannot yet be measured. We can therefore, in conclusion, 



478 NINETEENTH CENTUR Y. pt. hi. 

only try to understand the tendency of the science of our 
day as compared with that of earlier centuries. 

/ The work of the sixteenth century, as we saw (p. 81), 
was to overcome that blind worship of authority which had 
sprung up during the Dark Ages, and which is the greatest 
enemy to true knowledge. 

In the seventeenth century the march of scientific 
discovery began with Galileo, and advanced slowly but 
triumphantly through many dangers and difficulties till it 
culminated in the grand generalisations of Newton. This 
was the first great era of modern science, especially of astro- 
N. nomy and physics, though Biology also made a great stride 
when Harvey demonstrated the circulation of the blood. 

The eighteenth century continued the same work of 
patient inquiry, completing the harmony of astronomy by 
bringing the observed movements of the planets under 
Newton's law of gravitation ; founding chemistry upon a 
" . firm basis of careful experiment ; creating the sciences of 
zoology and botany, by establishing true systems of classi- 
fication ; discovering the hitherto almost unknown force of 
electricity; and reading in the crust of the earth the history 
of the past ages of our planet. 

And so, when the nineteenth century opened, men found 
themselves with an immense mass of known facts and 
careful experiments, which had been accumulated during 
the last two centuries, and which were very difficult to deal 
with, because it had become almost impossible for any single 
mind to grasp them all. The scientific men of our century 
/ have therefore become divided into two great classes. On the 
one hand men have devoted themselves to special sciences, 
and even to special branches of a science, so that a man 
will often spend his whole life in the study of one depart- 
ment of chemistry or physics, or in investigating one little 



ch. xlii. CONCLUDING REMARKS. 479 

group of insects ; and in this way discoveries of great value 
have been made. 

On the other hand, great minds among us have taken up j 
the separate facts collected by specialists, and have woven J ^ 
the whole of physical science into one grand scheme. Such { 
men as Faraday, Sir W. Grove, Stokes, Helmholtz, Sir W. 
Thomson, and Clerk-Maxwell, together with many others, 
have done their part in this work, so that now all the various 
physical .. forces have been shown to be probably phases of \J 
one great force appearing under many forms. For the future \ 
no one physical force can be studied as if it existed by itself 
alone, for each is shown to arise out of, and to pass into, 
others. Heat, electricity, magnetism, chemical affinity, 
motion — all are related to each other, and we cannot call 
any one of them the ruler over the rest. Like the colours on 
the soap-bubble, they each take their turn in appearing and 
disappearing, according to the conditions under which they 
arise. Their relations are almost infinitely complex, and 
we have still much to learn about them ; but the grand fact 
that they pass the one into the other has been demonstrated 
in our century ; and, under the names of ' the conserva 
tion of energy,' and ' the correlation of the physical forces, 
is one of the greatest results of modern science. 

The same tendency may be seen in the study of those 
sciences which relate to life. Here, again, modern investiga- 
tion links together the scattered observations of ages, and 
unites them all in the theory of ' evolution,' or the gradual 
unfolding of nature ; a theory which has been worked out 
in all its details by Herbert Spencer, one of our greatest 
living thinkers. In astronomy, indeed, we already catch 
a glimpse of this law in the probable formation of the 
heavenly bodies out of gaseous star-matter ; and in the or 
ganic world we find it even more firmly held by scientific 



480 NINETEENTH CENTURY. pt. hi. 

men in the belief that all the many forms of plant and 
animal life have been unfolded out of a few simple forms, 
just as the stem, the leaf, and the flower are evolved out of 
a simple seed. 

We need not be too eager to force the truth of this 
theory upon unwilling minds, for the history of science 
teaches us that nothing but truth can stand the test of long 
investigation, while no power or authority can resist in the 
end that which is true. The imperfect theory of phlogiston 
lid its work in gathering together many scattered facts in 
chemistry, and then died a natural death when the discovery 
-of oxygen threw more light upon the subject ; while no 
authority or persecution could suppress the true theory that 
the earth moves round the sun. 

It is of great importance that we should all learn this 
lesson, to have faith in the invincible power of truth ; for it 
would almost seem as if all the experience of past centuries 
had hardly yet convinced us. We still, like the Aristotelians 
and the judges of the Inquisition, often make hasty and 
ignorant assertions, and try rather to prop up by authority 
that which we believe, than to inquire earnestly whether it 
is true. Yet every page in the history of Science teaches 
the contrary lesson. So much as is true in any belief will 
stand because it is true ; while that which is mistaken will 
fade away before earnest and impartial examination. Our 
part is to endeavour, like the great men of whom we have 
been reading, to open our eyes to the laws which surround 
us, and which are only hidden from us by our ignorance. 
And from whatever source we derive our knowledge, we 
must remember that it is very little after all, and be ready 
at all times to examine new facts, even though they 
may seem to upset some of our favourite opinions ; for 
unless we are so foolish as to think we know everything, 



ch. xlii. CONCLUDING REMARKS. 481 

it is certain that we shall often find that we have been 
mistaken. 

Those who labour in this spirit of seeking the truth 
for itself will find their reward in the ever-increasing delight 
they will feel in studying God's works, and in the assurance 
which they will meet with at every step, that nothing can 
happen except under the guidance of His laws. True 
science, like true religion, leads to an entire and childlike 
dependence upon the Invisible Ruler of the Universe. It 
makes us eager to study the laws of the universe, that we 
may live in accordance with them, and diminish some of the 
gross ignorance which now prevails with all its attendant 
evils : while at the same time it leads even the most in- 
structed to feel how extremely limited our knowledge is, and 
that we are after all, like inexperienced children, dependent 
upon the love and power of our Maker to bring us safely 
out of darkness into light. 



CHRONOLOGICAL TABLES 

OF THE 

RISE AND PROGRESS OF THE VARIOUS 
BRANCHES OF SCIENCE. 



CHRONOLOGICAL TABLE. 



48S 



SCIENCE OF THE GREEKS. 

FROM B.C. 639 TO A.D. 200. 

The dates of this table refer to the years in -which each particular step in advance was 
made; but up to the end of the Middle Ages tkey must be regarded as merely 
approximative. 



Astronomy. 



B.C. 

600. Thales marks 
out solstices and 
equinoxes, p. 8. 

570. Anaximan- 
der — The sun- 
dial ; the phases 
of the moon, p. 9. 

500. Pythagoras 

— The earth 
moves ; morn- 
ing and even- 
ing star the 
same, p. n. 

450. Anaxagoras 

— Nature of 
sun and moon ; 
eclipses ; move- 
ments of the 
planets, p. 13. 

400. Democritus on 
Milky Way, p.15. 

360. Eudoxus on 
movements of 
the planets, p. 

357. Aristotle on 
occultation of 
Mars ; asserts 
that the earth is 
round, p. 15. 
Ecliptic and Zo- 
diac understood 
by the Greeks, 
p. 18. 

Aristarchus. 
Earth moves 
round the sun ; 
obliquity of 
ecliptic ; rota- 
tion of earth 
on its axi?, p. 20. 

130. Hipparchus 
on precession of 
the equinoxes ; 
calculates 
eclipses, p. 30. 



a.d. 100-170. Ptol- 
emy founds the 
Ptolemaic sys- 
tem, p. 32. 



Physics and 
Mechanics. 



500. Pythagoras 
invents the 
Monochord, p. 



260. Euclid on 
light travelling 
in straight lines, 
p. 21. 

250. Archimedes 
on the lever ; 
Hiero's _ crown 
and specific gra- 
vity ; screw of 
Archimedes, pp. 
22-25. 

20. Hero's en- 
gine, p. 244. 



Chemistry. 



Greeks knew how 
to extract iron, 
mercury, and 
other metals 
from the ore ; 
and make co- 
lours out of 
earths, p. 40. 



Physical 

Geography and 

Geology. 



570. Anaximan- 
der makes a 
map of the 
known world, p. 
10. 

500. Pythagoras 
on changes of 
land and sea ; 
on earthquakes, 
volcanoes, and 
petrifying 
springs, pp. 11- 



Biology. 



230. Eratosthe- 
nes lays down 
first parallel of 
latitude ; mea- 
sures circumfer- 
ence of the 
earth ; studies 
mountain 
chains, pp. 27- 



390. Hippocrates 
father of medi- 
cine ; separates 
medicine from 
the priesthood, 
p. 14. 

341. Aristotle 

founder of zoo- 
logy ; studies 

j the nature of 
plants and ani- 
mals, p. 16. 

340. Theophras- 
tus first bota- 
nist, p. 16. 

Erasistratus and 
Herophilus the 
first anato-j 
mists; theyj 
study brain ' 
muscles, and! 
nerves, p. 26. 



a.d. 100-170. Ptol- 
emy on geo- 
graphy, p. 33. 

Strabo on earth- 
quakes and vol- 
canoes, p. 33. 

Pliny on natural 
history, p. 33. 



a.d. 160. Galen, 
physician, 
studies nerves 
and arteries ; 
works out a 
theory of medi- 
cine, p. 34. 



4 86 



CHRONOLOGICAL TABLE. 



SCIENCE OF THE MIDDLE OR DARK AGES. 

FROM A.D. 700 TO 1500. 



Astronomy. 



The Arabs great 
astronomers, but 
mix up astrono- 
my with astro- j 
logy, p. 45. 



Physics and 
Mechanics. 



900. Albategnius 
calculates the 
length of the 
year, p. 45. 

1008. Ebn Junis 
draws up astro- 
nomical tables, 
p. 46. 



(900. Ben Musa 
on algebra and 
numerals.) 

(1000. Gerbert in- 
troduces Arabic 
numerals into 
Etirope.) 

1030. Alhazen on 
refraction of 
light ; on atmo- 
spheric reflec- 
tion ; on mag- 
nifying glasses, 
pp. 46-50. 



1240. Roger Ba- 
con and Viteflio 
on cause of the 
rainbow, p. 53. 

1302. Flavio Gio- 
ja invents the 
mariner's com- 
pass, p. 53. _ 

1455. Invention 
of printing, p. 
54- 

1480. Leonardo 
da Vinci makes 
water-mills and 
river-locks, p. 
58. 



Chemistry. 



800. Marcus 
Graecus makes 
gunpowder, p. 
42. 

Arabian alche- 
mists ; gases 
called 'spirit,' 
p. 41. 

860. Geber the 
founder of che- 
mistry ; distilla- 
tion and sub- 
limation ; makes 
nitric and sul- 
phuric acid ; 
discovers that 
heating a metal 
adds to its 
weight, pp. 43- 
45- 



Physical 

Geography and 

Geology. 



iiology. 



1240. Roger 
Bacon's experi- 
ments on air ; 
he makes gun- 
powder; his 
'Opus Majus' 
P- 52. 



)8o. Avicenna, a 
famous writer 
on minerals, p 
49. 



1492. Columbus 
discovers Ame- 
rica, p. 56. 
497. Vasco di 
G am a sails 
round the Cape 
of Good Hope ; 
sees the south- \ 
em stars, p. 57. j 



Arabs learn medi- 
cal science from 
Jews and Nes- 
torians, p. 40. 

700 to 800. Medi- 
cal schools of 
Bagdad and Sa- 
lerno flourish, 
p. 40. 

Arabs devote 
themselves t o 
medicine be- 
cause dissection 
is forbidden by 
the Koran, p. 40. 

920. Medical 
school of Cor- 
dova founded, 
p. 40. 



1030 Alhazen on , 
nature of sight ; j 
why we do not 1 
see double with j 
two eyes, pp. | 
47-49- 



CHRONOLOGICAL TABLE. 



487 



RISE OF MODERN SCIENCE. 

FROM A.D. 15 19 TO 1604. 



Astronomy. 


Physics and 
Mechanics. 


Chemistry. 


Physical 

Geography and 

Geology. 


Biology. 








1519. Magellan's 








1530. Paracelsus, 


ship sails round 








chemist and al- 


the world, p. 57. 


1542. Vesalius 


1543. Copernican 




chemist, sepa- 




refutes Galen ; 


system publish- 




rates out gold 




h i s anatomical 


ed, p. 64. 




by means of 




drawings, p. 65. 




1560. Baptiste 
Porta invents 
the camera ob- 
scura, p. 73. 


aquafortis, p. 
70. 


1565. Gesner on 


1548. Fallopius 
on anatomy, p. 
66. 

1551. Gesner, 
first zoological 
cabinet and 
botanical gar- 
den, p. 67. 

1560. Eustachi- 
us. — Eustachi- 
an tube, p. 66. 

1560. Porta on 
structure of the 
eye, p. 74. 

1565. Gesner's 


1575- Tycho 






mineralogy and 


'History of 


Brahe s obser- 






fossil shells, p. 


Animals,' p. 67 ; 


vatory on Huen 






68. 


His classifica- 


island ; Tycho- 








tion of plants, 


nic system, p. 
76. 
I57 6. Tycho in 








p. 68. 










Bohemia, P. 76. 


1580. P r t a's 
engine, p. 246. 




1580. Palissy, 
the potter, in- 






1583. Galileo on 




sists that fossil ii 5 8 3. C ae s a I- 




the pendulum, 




shells were once pinus classifies 




P' 77- 




real shells, p. plants by their 




1589. On falling 




214. 


flowers and' 




bodies, p. 78. 






seeds, p. 69. 




— On musical 










sound, p. 80. _ 










1592. On motion 










of heavy bodies, 






i 


1594. Kepler he- 


P- 79- „ . 








gins to study the 


1592. Stevmus 








planets, p. 93. 


on statics, p. 80. 








1597. He joins 










| Tycho in Bo- 










1 hernia, p. 93. 










1599 Rudolphine 










tables begun, p. 










93- 
1600. Bruno 


t6oo. Kircher in- 






1603. Fabricius 


burnt at the 


vents the magic 






discovers valves 


stake, p 82. 


; lantern, p. 74. 
1600. Gilbert 
1 makes experi- 
\ ments on elec- 






in veins, p. 109. 

1604. Kepler on 

formation of 

images on the 




! tricity, p. 75- 




retina, p 94. 



CHRONOLOGICAL TABLE. 



PROGRESS OF MODERN SCIENCE. 

FROM A.D. 1609 TO 1 642. 



Astronomy. 



1609. Galileo dis- 
covers second- 
ary light of the 
moon, Jupiter's 
moons ; phases 
of Venus, pp. 
87-90. 

1609. Kepler's 
two first laws, 
pp. 95-97 

1611. Galileo ob- 
serves sun-spots 
and proves ro- 
tation of sun on 
its axis, p. 90. 

1618. Kepler's 
third law, p 



Physics and 
Mechanics. 



ChemLtry. 



1628. Keplercom- 
pletes Rudol- 
phine tables, 
and foretells 
transits of Venus 

I and Mercury, 

i I' I54 ' r A- 

163 1. Gassendi 

observes transit 
of Mercury, p. 
154- 

1632. Galileo's 
system of the 
world ; his re- 
cantation, p. 91. 

1639. Horrocks 
observes transit 
of Venus, p. 
154- 

1642. Death of 
Galileo and 
birth of New- 
ton, pp. 92-144. 



609. Invention 
I of the telescope, 
! p. 85 ; Galileo's 
j telescope, p. 86. 



I 

,1611. Kepler's 
I telescope, p. 94. 
ji 6 1 5. Solomon 

Caus' engine, 

p. 244. 



1620. Drebbel 
alcohol thermo- 
meter, p. 118. 

1620. Bacon's 
'Novum O r- 
ganum,' p. 101 ; 
Bacon suggests 
that heat may 
be a movement, 

P- 349- 

1621. Snelhus 
discovers law 
of refraction, p. 
104. 1624. Van Hel 

1625. De Domi- mont introduces 
nis explains the j the term gas, p. 
rainbow, p. 161. 71 



Physical 

Geography and 

Geology. 



Biology. 



; i637. _ Descartes 
I on light and re- 

fraction, pp. 

104-161. 



i6ig. Harvey 
discovers circu- 
lation of the 
blood, pp. 108- 



1622. Asellius 
discovers lac- 
teals, 112. 



CHRONOLOGICAL TABLE. 



489 



PROGRESS OF MODERN SCIENCE. 

FROM A.D. 1638 TO 1670. 



Astronomy. 


Physics and 
Mechanics. 


Chemistry. 


Physical 

Geography and 

Geology. 


Biology. i 




1638. Galileo on 






1 




musical notes, p. 


(1645. First 




1 




80. 


meetings of 




| 




1644. Torricelii 


Royal Society, 








invents the ba- 


p. 122.) 




1647. Pecquet 




rometer, p. 116. 






on the thoracic ! 




1646. Pascal 






duct, p. 113 j 




proves the 






1649. Riidbeck | 




weight of air, 






discovers lym-i 




p. 117. 






phatics, p. 113. j 
1656. Malpighi | 




1650. Guericke 






professor of me- 




invents the air- 






dicine at Bo- 




pump : Magde- 






logna, p. 135. 




burg hemi- 










spheres: first 










electrical m a - 








1659. Huyghens 


chine, pp. 119- 








discovers Sa- 


121. 








turn's ring, and 


165S. Huyghens 








one satellite, p. 


n cycloidal 






166 1. Malpighi 
uses microscope 


175- 


pendulums, p. 


(1662. AcadSmie 
des Sciences 






i75- _ , , 




to examine air- 




1661. Boyle s 


f un de d, p. 




cells of the 




law of compres- 


124.) 




lungs ; discovers 


1666. Newton 


sion of gases, p. 






Malpighian 


n method f 


126. 






layer: studies 


fluxions; first 








anatomy of in- 


idea of gravita- 








sects, pp. 135- 


tion, pp. 145- 








137. 


150. 








1663-1666. Jour- 
neys of Ray and 
Willughby, p. ! 




1663. Marquis 


1665. Hooke on 




I 39« 




of Worcester's 


use of air in 








engine, p. 244. 


combustion, p. 
128. 
1665. Boyle's ex- 
periments on 
air, p. 126. 








1666-1671. New- 










ton on disper- 










sion of light, 




1669. Steno on 






proves its com- 




fossils and petri- 






pound nature, 




factions, p. 214. 






pp. 161-166. 


1670. Mayow 


1670. Scilla on 


1670. Mayo w 




1670. First mer- 


discovers ' fire- 


fossils of Cala- 


on respiration, 




curial thermo- 


air,' and shows 


bria, p. 214. 


p. 132. 




meter, p. 118. 


it is used in 
burning, p. 129. 
1670. Beecher 
proposes theory, 
of 'phlogiston.' 
p. 132- 




1 



49o 



CHRONOLOGICAL TABLE. 



PROGRESS OF MODERN SCIENCE. 

FROM A.D. 1674 TO I 7 2 9. 



Astronomy. 


Physics and 
Mechanics. 


Chemistry. 


Physical 

Geography and 

Geology. 


Biology. 










1674. Malpighi 


1676. Halley ob- 


1676. Roemer 






on structure of 


serves transit of 


measures velo- 






plants, p. 137. 


Mercury, p. 


city of light, p. 






1677. Leeuwen- 


154- 


172. 
1676. Noble and 
Pigot on stretch- 
ed strings, p. 263. 






hoeck discovers 
animalcules, p. 
136. 


1682. Newton 


1678. Huyghens 




1682. Picart'1682. Grew on 


works out and 


proposes undu- 




measures the structure of 


publishes the 


latory theory of 




size of the earth, 


plants, p. 137. 


law of gravita- 


light ; law of 




p. 147- 




tion, pp. 147- 


double refrac- 








152. 


tion, pp. 175-179. 








1682. Halley 










foretells the re- 










turn of a comet, 










P- i59- T 
1687. Newton s 


1687. Newton 








' Pri nci pia ' 


on propagation 






published, p. 


of sound, p. 166. 








150. 


1690. Papin's 
heat-engine, p. 






1690. Rivinus 


1691. Halley's 


245- 






proposes to give 


method of mea- 








two names to 


suring the sun's 








each plant, p. 


distance by the 








208. 


transit of Venus, 








1693. Ray and 
WUlughby's 


P- 155- 
















classification of 




1698. Savery's 






animals ; Ray's 




heat-engine, p. 






system of plants, 




245- 






pp. 138-142. 




1700. Sauveur 






1694. Tourne- 




on musical vibra- 




1695. Woodward fort's system of 




tions, p. 263. 




on fossils and plants, p. 142. 




Bernoulli, Euler, 


1 701. Boerhaave 


succession of 




Lagrange on 


founder of or- 


formations in 






musical strings, 1 g a n i c chemis- 


England, p. 






p. 263, etc. 


try, pp. 191-194. 


215. 11707- Buff on and 




1705. Newco- 






Linnaeus born, 




men's engine, 


1718. Hales's ex- 




p. 203. 


1722. Graham on 


p. 244. 


periments on 






shifting of mag- 




gases, p. 225. 






netic needle, p. 










3 80. 
1727. Bradley on 








1727. Hales on 


nutation and 1729. C. More 


1729. S t a h 1 




respiration of 


aberration, p. Hall on disper- 


founds a system 




plants and for- 


2 75« 


sion of light in 


of chemistry on 




mation of sap, 




flint and crown 


the theory of 




P- 193- 




glass, p. 166. 


phlogiston, p. 






1732. Du Faye 


133- 1 








on electricity, 










P- 253. 






1 



CHRONOLOGICAL TABLE. 



49 1 



PROGRESS OF MODERN SCIENCE. 

FROM A.D. 17^8 TO 1767. 



Astronomy. 



Physics and 
Mechanics. 



Chemistry. 



Physical 

Geography and 

Geology. 



Biology. 



i 73 8. Bougier 

makes the hrst 
attempt to mea- 
sure the earth's 
density, p. 208. 



1761. Sun's dis- 
tance first mea- 1 
sured by the j 
transit of Ve- j 
nus ; Delisle's j 
method intro- 
duced, pp. 155 ! 
and 276. 

1764-1780. La- 
grange, libra- 
tionof the moon, 
p. 277. 



840. Hawksbee's 
electrical ma- 
chine, p. 121. 



744. Celsius, 
Fahrenheit, and 
Reaumur mark 
off degrees on 
thermometer, p. 
118. 

746. Franklin's 
experiments in 
electricity, p. 
253- 



1752. Franklin 
proves identity 
of electricity 
and lightning, 
P- 255- 



1757. Dollond's 
achromatic tele- 
scope, p. 166. 

1760. Black on 
latent heat in 
melting ice and 
in steam, p. 240. 



765. Watt's 
steam - engine, 
pp. 242-247. 



1738. Bernouilli 
on molecules of 
gases, p. 362. 



740. Lazzaro 

Moro on the 
formation of the 
crust of the 
earth, p. 215. 



1756. 'Black ex- 
tracts ' fixed 
air' from lime- 
stone and ex- 
amines it, p. 225. 

1761. Bergmann 
on chemical af- 
finity and 'tests;' 
proves that 
fixed air is an 
acid, p. 227. 



1766. Cavendish 
discovers hy- 
drogen, p. 229. 



1749. Hutton be- 
gins to examine 
the formations 
of the earth's 
crust, p. 218. 



1741. _ Linnaeus' 
botanical gar- 
den at Upsala, 
p. 207. 

1743. Haller on 
contraction of 
the muscles ; 
anatomical 
plates, p. 195. 



1748. Haller and 
Hunter on com- 
parative ana- 
tomy, p. 196. 

1749. Buffon's 
' Natural His- 
tory;' distribu- 
tion of animals, 
p. 204. 

750. Dauben- 
ton's anatomy, | 
p. 204. 

753. Linnaeus 1 
introduces spe- j 
cine names, p. 1 
207. 

754. Bonnet on | 
leaves of plants, 
p. 200. 



1762. Bonnet and 
Spallanzani on 
regrowth of se- 
vered limbs, p. 
200. 

1764. Bonnet on 
development of 
animate, p. 202. 



1767. Sprengel 
on fertilisation 
of plants, p. 415- 



492 



CHRONOLOGICAL TABLE. 



PROGRESS OF MODERN SCIENCE. 

FROM A.D. 1766 TO I 7 89. 



Astronomy. 



Physics and 
Mechanics. 



Chemistry. 



1774. Maskelyne 
measures the 
earth's density 
by Schehallion 
experiment, p. 
288. 

1774-1783. La- 
place on long 
inequality of 
Jupiter and Sa- 
turn ; moon's 
acceleration, pp. 
277-280. 

1776. Lagrange 
proves the sta- 
bility of the 
planetary or- 
bits, p. 280. 



1781. Uranus 
discovered by 
Herschel,p. 281. 

1783. Proves the 
rotation of bi- 
nary stars, p. 
283. 



1786. He dis- 
covers star-clus- 
ters and nebu- 
lae, p. 284 ; and 
the motion of 
the solar sys- 
tem towards 
Hercules, p. 
285. 



1769. Boulton 
and Watt part- 
ners, p. 256. 



1785. Chladni on 
musical vibra- 
tions of solid 
bodies, p. 269. 

1785. Watt's 
double - acting 
steam - engine, 
p. 250. 



1789. Electricity 
experiments of 
Galvani ; con- 
troversy between 
Volta and Gal- 
vani, pp. 257- 
262. 



Physical 

Geography and 

Geology. 



1772. Rutherford ( 
describes nitro- 
gen, p. 234. 

1774. Priestley- 
discovers oxy- 
gen, p. 230. 



1766. Cook's 
voyage to the 
South Seas for 
the second tran- 
sit measure- 
ment, p. 159. 



177S. Scheele dis- 1775. Werner lec- 
covers oxygen, 1 tures on geo- 
p. 230. I logy at Frey- 

i berg, p. 216. 



1778. Lavoisier 
overthrows the 
theory of ' phlo- 
giston ' by prov- 
ing the action 
of oxygen, p. 
234. 

1779. Shows the 
composition of 
carbonic acid, 
P- 237. 



1784. Cavendish 
explodes oxy- 
gen and hydro- 
gen, forming 
water, p. 230. 

1787. Lavoisier 
founds a new 
chemical nomen- 
clature, p. 239. 

1789. Lavoisier's 
' Elements of 
Chemistry' pub- 
lished, p. 238. 



784. Disputes 
between Nep- 
tunists and Vul- 

j canists. p. 217. 

1785. Sir James 
Hall on melted 

I rock ; Hutton 
on granite veins, 
p. 221. 

1788. Hutton's 
'Theory of the 
Earth ' publish- 
ed, p. 218. 



Biology. 



1768. Foundation 
of the Linnsean 
system ; * Sys- 
tema Naturae ' 
completed, pp. 
207-211. 

1772. Priestley 
on breathing of 
plants, p. 231. 



773. Death of 
Linnaeus ; his 
collections 
brought to Eng- 
land, p. 211. 



1783. Hunter's 
museum begun 
in Leicester 

Square, p. 199. 



1789. Animalelec- 
tricity discover- 
ed by Galvani, '■ 
p. 257. m 1 

1789. Jussieu : 

founds the Na- 1 
tural System of; 
plants, p. 412. 1 



CHRONOLOGICAL TABLE. 



493 



PROGRESS OF MODERN SCIENCE. 



FROM A.D. 1790 TO I 8 I I, 



Astronomy. 


Ph}'sics and 
Mechanics. 


Chemistry. 


Physical 

Geography and 

Geology. 


Biology. 








1790. Wm. Smith 


1790. Goethe on 








studies the suc- 


the metamor- 








cession of strata, 


phosis of plants, 








P> 221 -^ „ 


p. 413. 








1790. De Saus- 






1792. Voltaic or 




sure studies the 




1793. Herschel 


chemical elec- 




action of gla- 




on cause of sun- 


tricity, p. 259. 


1794. Lavoisier 


ciers, p. 449. 




spots, p. 379. 


1798. Rumford 
boils water by 
friction, p. 351. 


guillotined, p. 
238. 






1799. Laplace's 


1799. Davy melts 




1799. Humboldt's 




' ivl € c a n i q u e 


ice by friction, 




journeys in 




Celeste,' p. 281. 


P- 352. 




America. He 






1800. Voltaic 


1800. Nicholson 


traces isother- 


1800. Cuvier's 




pile, p. 261. 


and Carlisle, de- 


mal lines, p. 


lectures on ana- 




1800. Sir W. Her- 


composition of 


423- 


tomy ; he in- 




schel discovers 


water, p. 392. 




sists on the fit- 




dark heat-rays, 


1800. Davy on 




ness of organisa- 




P- 33o- 


laughing gas, 




tion in indi- 


1801. Piazzi dis- 


1801. Ritter dis- 


P- 39i- 




vidual animals, 


covers Ceres, 


covers chemical 






pp. 27-437. 


the first of the 


rays, p. 331. 






1 801. Lamarck 


asteroids, p. 299. 


1 801. Young on 
interference of 






on development 
of animals, p. 


1802-4-7. Dis- 


light, p. 324. 
1802. Wedgwood 






429. 


covery of other 


and Davy, sun- 








asteroids. Ol- 


pictures, p. 331. 






1802. G. St. -Hi- 


bers suggests 


1802. Wollaston, 






lairs brings zoo- 


they are frag- 


lines of spec- 






logical collec- 


ments of a 


trum, p. 333. 






t i on s from 


planet, p. 300. 








Egypt, p. 428. 


1803. Biot on me- 


1804. Fraunhofer 








teoric stones, p. 


compares lines 


1806. Davy on 






3°7- 


in the spectrum 


electrolysis ; 








of sun and stars, 


discovers potas- 




1804. Humboldt ! 




P- 334- 


sium and so- 
dium, p. 392. 

1S08. Dal ton, 
law of multiple 
proportions ; 




on distribution 
of plants, p. 424. 




1808. Malus dis- 


atomic theory, 








covers polariza- 


pp. 399-403. 








tion of light by 


1808. Gay Lus- 








reflection, p. 


sac on combina- 








3x8. 


tion in multiple- 
volumes, p. 404. 








1811. Leslie and 


181 1. Avogadro 








Melloni on heat 


on molecular 








rays p. 359. 


composition of 

gases, p. 405. 







494 



CHRONOLOGICAL TABLE. 



PROGRESS OF MODERN SCIENCE. 

FROM A.D. l8l2 TO 1 848. 



Astronomy. 


Physics and 
Mechanics. 


Chemistry. 


Physical 

Geography and 

Geology. 


Biology. 








1812. Former 


1 
181 2. Cuvier re- 








periods of life 


stores the fossil 








on the globe 


animals of Paris, 








proved by 


P- 435- 








Cuvier, p. 435. 






18 1 5. Davy's 




1815. W. Smith's 






safety- lamp, p. 




geological map, 






39 1 - 




p. 221. 






1816. Fresnel 










and Young, po- 




1817. Buckland's 


1817. Cuvier's 




larization ol 




geological lec- 


' Animal King- 




light, p. 324. 


1818. Berzelius 


tures, p. 442. 


dom ' published, 
P- 433- 
1818. G. St.-Hi- 


1819. Encke's 


1819. Oersted, 


on use of the 




laire on unity of 


Comet, p. 300. 


electro -magnet- 


blow - pipe, p. 




plan in animals, 




ism, p. 367. 


398. 




P- 43i- 


1820-1838. Sir J. 


1820. Ampere, 








Herschel studies 


electro-magnet- 








stars of the 


ism, p. 370. 








southern hemi- 


1 821. Faraday, 








sphere ; Magel- 


electro -magnet- 








lanic clouds, p. 


ism, p. 376. 
1822. Seebeck on 








3°5- 


1822. Herschel 








thermo - electri- 


on use of spec- 








city, p. 377- . 


troscope to de- 


1825. McEnery 




1826-60. Schwabe 


1826. Nobili 


tect chemical 


discovers flint 




proves periodi- 


proves the 


elements, p. 338. 


tools, with bones 


1828. Von Baer's 


city of sun- 


truth of animal 




of extinct ani- 


law of embryo- 


spots, p. 379. 


electricity, p. 




mals, in Kent's 


logical develop- 


1826. Biela's 


259- 


1823. Liquefac- 


Cavern, p. 453. 


ment, p. 437. 


comet, p. 301. 




tion of gases by 
Faraday, p. 406. 










1830. Liebig's 


1830. Lyell's 'Geo- 


1830. Robert 






analyses of or- 


logy ; ' he in- 


Brown, Molden- 






ganic sub- 


sists on suffi- 


hauer, Mirbel, 






stances, p. 408. 


ciency of causes 


and others, on 






1832. Discovery 


like the present 


structural and 






of chloroform 


to explain the 


physiological bo- 






and chlorale by 


past history of tany, pp. 4T7-20. 




1837. Wheatstone 


Liebig, p. 409. 


the globe, p. 1832. Death of 


1838. Herschel's 


and Cooke elec- 




442. 


Cuvier, p. 422. 


' Outlines of As- 


tric telegraph, 


1834. Faraday on 




1839. Agassiz 


tronomy' pub- 


p. 382. 


electrolysis ; 




on freshwater 


lished, p. 305. 




chemical nature 
of electric cur- 




fishes, p. 447. 




1839-42. Seguin 


rent ; invention 


1840. Agassiz on 


1840-48. Organic 




and Mayer on 


of voltameter, 


glacial period 


chemistry, p. 




relation between 


P- 395- 


and blocks car- 


408. 1 




heat and work, 




ried over Eu- 1835. Sir W. \ 




P- 35:- 




rope by ice, p. 


Hooker, and 




1839. Daguerreor 




44 8. 


foundation of 




types, p. 332. 






Kew Gardens, 
p. 421. 



CHRONOLOGICAL TABLE. 



495 



RISE OF MODERN SCIENCE. 

FROM A.D. 1843 TO 1 879. 



Astronomy, 



Physics and 
Mechanics, 



1845. Division of 
Biela's comet, 
p. 3°*- , 

1845-46. Adams 
and Leverrier 
work out the 
position of Nep- 
tune; Galle finds 
the planet, pp. 
302-304. 

1850. Lamont, 
periodicity of 
magnetic dis- 
turbance, p. 380. 



1859. Carrington 
and Hodgson, 
sun - spot and 
magnetic dis- 
turbance, p. 381. 

1859. Lescarbault 
seesintra-mercu- 
rial planet, p. 3 12. 



1862-66. Schiape- 
relli, Adams, 
and Leverrier, 
discover the or- 
bits of comets 
and meteor sys- 
tems, p. 308. 

1862. Travelling 
stars studied by 
the spectroscope, 
p. 346. _ 

1874. Expeditions 
to observe the 
transit of Venus, 
P- 159- 

1875. Leverrier's 
analysis of the 
orbits of the 
planets, p. 312. 

1877. Discovery 
of satellites of 
Mars, by Asaph 
Hall, p. 311. 

1878. Watson 
sees two intra- 
mercurial pla- 
nets, p. 312. 



1843-49. . Joule 
on equivalent 
of heat ; dyna- 
mical theory of 
heat, p. 354. 

— Hirn's experi- 
ments on heat, 
P- 358. , , 

1847. Helmholtz, 
conservation of 
energy, p. 360. 

1850. Foucault 
and Fizeau on 
velocity of light, 

P- 3 2 7- , , 
18—. Clerk-Max- 
well and others 
on molecular 
theory of gases. 
Helmholtz and 
Sir W. Thomson 
on vibrations of 
molecules, pp. 
362-365. 
1852. Thomson, 
Sir W., dissipa- 
tion of energy, 
P- 360. 
1860-1866. Four 
new metals dis- 
covered by spec- 
trum analysis, 
P- 338. 

1861. Bunsen and 
Kirchhoff dis- 
cover the mean- 
ing of the lines 
in the spectrum, 
P- 338. . 

1862. Hugginsand 
M i 1 1 e r, s p e c- 
trum analysis 
of the stars and 
nebulae, p. 343. 

— Alexander 
Herschel, spec- 
trum of falling 
stars, p. 345. 

1872. Graham 
Bell, the tele- 
phone, p. 387. 

1878. Abney on 
photography at 
the red end of 
the spectrum, p. 
333- 



Chemistry. 



:8 4 3. Wohler 
makes organic 
elements artifi- 
cially, p. 408. 



1850 et seq. Ad- 
vances in chem- 
istry of organic 
compounds, p. 

409. 



861. Metals in 
the atmosphere 
of the sun and 
stars discovered 
by spectrum 
analysis, p. 341. 

862. Andrews 
on critical points 
in gases, p. 406. 



[877-78. Pictet 
and Cailletet 
liquefy the per- 
manent gases, 
p. 407. 

[879. Crookes on 
ultra - gaseous 
state of matter, 
P- 365- 



Physical 

Geography and 

Geology. 



[847. Boucher de 
Perthes dis- 
covers flint im- 
plements at 
A b b e v i 1 1 e, p. 
452. 



853. Discovery 
of Swiss lake- 
dwellings, p. 
454- 

858. Humboldt's 
'Cosmos' pub- 
lished ; death of 
Humboldt, p. 
423- 



1863. 'Antiquity 
of Man,' p. 452. 



Biology. 



840. Miiller, 
Sachsandothers 
on structural 
botany, p. 472. 



853. Von Mohl 
on protoplasm, 
p. 420. 



858. Theory of 
natural selec- 
tion by Darwin 
and Wallace, 
p. 463. 



1859. Darwin's | 
' Origin of Spe- 
cies, p. 464. 

—Structure of 
carnivorous 
plants, p. 472. 



1852-72. D i s- 
covery of inter- 
mediate fossil 
forms, pp. 460- 

476. 

1860-79. Advance 
in our knowledge 
of fertilisation of - f 

plants, p. 474. f/c*J tz/l * A ' 

1878. Professor 
Marsh's disco- 
veries of gigan- 
tic fossil forms 
in America, p. 
476. 



1 



f 




'o 


Hippocrates ; Aristotle ; 
Theophrastus ; Erasis- 
tratus ; Herophilus ; 
Galen. 


•3 

1 

i 


Vesalius ; Fallopius ; Eu- 
stachius ; Gesner ; Cse- 
salpinus ; Fabricius. 


Harvey ; Asellius ; Riid- 
beck ; Malpighi ; Leeu- 
wenhoeck ; Grew ; Ray ; 
Willughby; Tournefort. 


Boerhaave ; Hales ; Hal- 
ler ; Hunter ; Bonnet ; 
Spallanzani ; Buffon ; 
Daubenton ; Linnaeus ; 
Jussieu ; Sprengel. 


Lamarck ; Goethe ; G. St.- 
Hilaire ; Cuvier ; Von 
Baer ; Boucher de 
Perthes ; Darwin ; Wal- 
lace; Agassiz; Auguste 
de Candolle; R. Brown ; 
Von Mohl; Sir W. 
Hooker ; Owen ; Hux- 
ley ; Parker ; Balfour ; 
Ha:ckel ; Gegenbaur. 


T3 

3 

a 
>> 

A 
°- . 

%o° 

10 

>. 


Anaximander. 

Pythagoras. 

Eratosthenes. 

Ptolemy 

Strabo. 


Avicenna. 
Columbus. 
Vasco di Gama. 
Magellan. 


a ui 

3.2 


1 

£== 8 

<ncn> 


Lazzaro Moro. 
Werner. 
Hutton. 
William Smith. 
De Saussure. 


Humboldt. 

Buckland. 

Lyell. # 

Agassiz. 

Murchison. 

Sedgwick. 

Von Buch. 

Prestwich. 


J* 




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INDEX 



ABBEVILLE 

ABBEVILLE flint implements, 453 
Aberration of fixed stars, 275 
Abney, Capt., on chemical rays of light, 

333 

Academies of science founded, 124 

' Academy of Secrets ' at Naples, 73 

Achromatic telescopes, 166 

Acids, strong, discovered by Geber, 44 

Acoustics, Newton on, 166 ; Chladni on, 
269 

Adams calculates the position of Neptune, 
302 ; on November mrteors, 309 

.<Esculapius, god of medicine, 14 

Aerial acid, Bergmann on, 228 

Agassiz, his history, 447 ; on glacial period, 
448 

Aigle, meteoric stone-fall at, 307 

Air, Boyle and Hooke, experiment on, 
128 ; Mayow on, 129 ; -cells studied by 
Malpighi, 138; -pump, section of, 119; 
-tubes of insects, 136 

Airy, Adam's paper on Neptune sent to, 303 

Albategnius calculates length of year, 45 

Albinus, anatomical drawings of, 196 

Alchemists, Arabian, 40 

Aldebaran, spectrum of, 344 

Alexandria, founding of the city of, 18 ; 
school of learning at, 18 ; taken by the 
Arabs, 39 ; Egyptian animals preserved 
at, 428 

Algebra, an Arabian name, 46 

Alhazen on eyesight, 46 ; on refraction, 
47 ; on atmospheric refraction, 48 ; on 
magnifying power of lenses, 49 

Alps, glaciers of the, 448 

Al Sufi estimates brilliancy of the stars, 45 

Amazons, closely related butterflies of the, 
458 

Amber, electric nature of, 74 

America, glaciation of, 451 

Ammonia, origin of name, 45 

Ampere, early life of, 369 ; on direction of 
magnetic current, 371 ; on electro-mag- 
nets, 372 ; invents the galvanometer, 
377 ; on cause of terrestrial magnetism, 
377 ; suggests electric telegraph, 382 ; 
on pressure of gases, 405. 



ARAGO 

Analysis, term explained, 399 ; of sub- 
stances by tests, 397 ; spectrum-, 338, 398 

Anatomy, Erasistratus and Herophilus on, 
26 ; Vesalius on, 65 ; Eustachius and 
Fallopius on, 66 ; vegetable-, 138 ; rise of 
comparative, 197 ; Haller and Hunter 
on, 197 ; Cuvier on, 432. 

Anatomical plates of Vesalius, 65 ; of 
Haller, 196 

Anaxagoras on the moon and on eclipses, 
13 ; banished, 14 

Anaximander, science of, 9 

Anderson brings Newcomen engine to 
Watt, 244 

Andrews on critical point of gases, 406 ; 
cited, 363 

Angstrom on the solar spectrum, 343 

Aniline dyes, 410 

Animal electricity, 257 

Animalcules, discovery of, 136 

Animals, Cuvier on internal structure of, 
434 ; fossil, restored by Cuvier, 435 ; La- 
marck on development of, 429 ; facts prov- 
ing development of, 457, etc. ; gradual 
succession of, on the globe, 460 ; selec- 
tion of, by man, 466 ; natural selection of, 
466 ; fossil, intermediate forms of, 476. 

Animals and plants, Aristotle on links 
between, 16 ; history of, by Gesner, 67 ; 
classified by Ray and Willughby, 140 ; 
Linnseus gives specific names to, 209 ; 
Buffon on distribution of, 205 ; Grew and 
Malpighi on, 134-138; Darwin and 
Wallace on, 463 

Antiquity of man, 452 

Aphides, Bonnet on, 200 

Apollo or Helios, god of the sun, 17 

Apple, Newton and the, 146 ; -leaf, skin of, 
showing stomates, 138 

Aqueous rocks, Hutton on, 218 

Arabs, conquests of the, 39 ; science of the, 
40 ; chemistry of the, 40 ; gunpowder 
known to the, 42 ; medical schools of 
the, 40 

Arago on polarisation of light, 324 ; on 
electro-magnetism, 373 ; on Biela's comet. 
301 



498 



INDEX. 



ARCHIMEDES 

Archimedes on the lever, 22 ; on Hiero's 
crown and specific gravity, 22 ; screw of, 
25 ; killed in the Punic war, 25 

Areas described by planets about their 
centre, 97 

Aristarchus taught that the earth moves 
round the sun, 20 ; discovered obliquity 
of ecliptic, 21 ; and rotation of the earth 
on its axis, 21 

Aristotelians, dogmatism of the, 78, 103 

Aristotle on astronomy and zoology, 15, 16 ; 
on development of animals, 457 

Arteries, passage of blood in, 109 ; throb- 
bing of, explained, no 

Asellius on lacteals and nourishing fluid, 
112 

Astatic needle of the telegraph, 385 

Asteroids, or minor planets, 299 

Astrology of the Arabs, 45 

Astronomy, definition of, 2 ; of Thales, 8 ; 
of Anaximander, 9 ; of Anaxagoras, 13 ; 
of Aristotle, 15; of Aristarchus, 20; of 
Hipparchus, 29 ; of Ptolemy, 32 ; of 
Albategnius, 45 ; of Ebn Junis, 45 ; of 
seventeenth century, 182 ; of eighteenth 
century, 275 ; of nineteenth century, 298 

Atmosphere, refraction of sun's rays in the, 
48; varying weight of the, 116; pressure 
of the, 120 

Atomic theory, 4c 2 

Atoms, definition of term, 402 ; of all the 
planets attract each other, 148 

Attraction, by electricity, 75, 122 ; of 
gravitation decreases with square of the 
distance, 150 

Aurora borealis coincident with outbreak 
of a sun-spot, 381 

Australia, fossil and living pouched animals 
of, 460 

Authority valued more than truth in the 
Dark Ages, 103 

Avicenna on minerals, 49 

Avogadro on gases, 405 

DACON, Roger, his ' Opus Majus,' 52 
-*-' Bacon, Francis, his influence on 

science, 101 ; on heat, 349 
Baer. See Von Baer 
Bagdad, medical school of, 40 
Bain's telegraph, 386 
Balfour, Francis, on morphology, 440 
Balloons, hydrogen used for filling, 230 
Hanks, Sir J., his museum, 418 
Barometer, invention of the, 114, 117 
Bartholinus on double refraction in Iceland 

spar, 179 
Bary, de, cited, 474 

Basalt, disputes about formation of, 217-200 
Bates on species of Amazon insects, 458 
Battery, first eiectric, 260 
Bccher proposes theory of Phlogiston, 133 
Liecquerel cited, 378 



BROUGHAM 

Beehive, star-cluster called the, 284 

Bees, clover fertilised by, 467 

Bell on the telephone, 338 

Bells, cause of musical sound in, 272 

Ben Musa, Arabian mathematician, 45 

Benzole discovered, 410 

Bergmann on chemical affinity, 227 ; on 
'fixed air,' 228 

Bernoulli on gases, 362 ; on stretched 
strings, 263 

Berzellius — His discoveries by electrolysis, 
394 ; on use of blowpipe, 358 

Betelgeux, no hydrogen in light of, 344 

Biela's comet, 301 

Binary stars, Herschel discovers, 284 

Biology, definition of, 2 ; of seventeenth 
century, 185 ; spread of, in eighteenth 
century, 190 

Biot on meteoric stone-fall, 307 ; on polari- 
zation, 327 

Birds, Ray and Willughby on, 138 ; rapid 
multiplication of, 466 

Black discovers ' fixed air,' 225 ; on latent 
heat, 240 

Blood, circulation of the, 109-111 ; earlier 
theories about, 108 ; air - bubbles drawn 
out of the, 132 

Blowpipe, Berzellius on use of. 398 

Blumenbach cited, 411 

Bode's law, 299 

Boerhaave, his character and influence, 
191 ; on organic chemistry, 192 ; on 
juices of plants, 192; on fluids of animals, 
194 ; his death, 194 

Bonnet's experiments on aphides and 
plants, 200 ; on regrowth of severed 
limbs, 200 ; on development of animals, 
202 

Bornet, Professor, cited, 474 

Botanical garden of Gesner, 67 

Botanist, Theophrastus the first, 16 

Botany, different kinds of, 2 ; writers on, 
17, 68, 69, 141, 207, 412 

Boucher de Perthes finds ancient flint im- 
plements, 452 

Bougier measures the densitv of the earth, 
288 

Boulton, partner of Watt, 250 

Boyle one of the founders of Royal Society, 
123 ; his air-pump, 126 ; his law of com- 
pressibility of gases, 117 ; his experiments 
on air, 128 

Bradley, 188; on aberration and nutation, 275 

Brain described by Erasistratus, 26 

Breathing, Mayow on, 131^ 

Brewster, Sir D., on polarization, 327 ; on 
spectrum analysis, 338 

British Museum, meteoric stones in the, 

3°7 
Bronze tools of lake-dwellings, 454 
Brougham, Lord, his article against Young, 

324 



INDEX. 



499 



BROWN 

Brown, Robert, on structural botany, 418 

Bruno burnt at the stake, 81 

Buckland, his Cambridge lectures, 442 ; on 
glaciation of Wales, 451 

Buffon, history of, 203 ; his work on na- 
tural history, 204 ; patronises Lamarck, 
427 

Bunsen on dark lines in solar spectrum, 339 

CjESALPINUS on plants, 69 ; on cir- 
culation of the blood, 109 

Caesium discovered, 338 

Cailletet, M., liquefies permanent gases, 407 

Cairo, medical school of, 40 

Caloric, old term for heat, 350 

Camera obscura, invention of the, 73 

Candolle, Auguste de, on natural system 
of plants, 413 

Capillaries discovered by Malpighi, 135 

Carbonic acid obtained by Black, 225 ; 
tested by Bergmann, 228 ; its nature dis- 
covered by Lavoisier, 237 

Carlisle on decomposition of water by 
electricity, 392 

Carnivorous plants, 472 

Carnot on heat converted into motion, 358 

Carrington, Mr., on outbreak of a sun-spot, 
381 

Cassini on velocity of light, 173 

Catastrophists in geology, 441 

Cats, their indirect influence on growth of 
clover, 467 

Caus' engine, 244 

Cavendish discovers hydrogen, 229 ; on 
composition of water, 230 ; his experi- 
ment on weight of the earth, 289 

Caxton the printer, 55 

Celestial photography, 347 

Cellular tissue, section of, 137 

Celsius invents centigrade scale, 118 

Centigrade scale, 118 

Ceres discovered by Piazzi, 299 

Challenger, forms brought home by the, 477 

Charles II. grants Royal Society charter, 
123; V. of Spain protects Vesalius, 66 

Chemical rays discovered, 331 ; action of, 
in photography, 332; nomenclature of 
Lavoisier, 238 ; elements, weight of, 401 ; 
symbols, 404 : theory of electricity, 395 

Chemical affinity, Bergmann on, 227 ; 
Newton on, 227 ; power of electric cur- 
rent to overcome, 395 

Chemistry, definition of, 2 ; of the Arabs, 
41 ; of Geber, 43 ; of Paracelsus and Van 
Helmont, 70 ; of Boyle and Hooke, 128 ; 
of Mayow, 129 ; Boerhaave on organic, 
192 ; of Black, 225 ; of Bergmann, 227 ; 
of Cavendish, 229 ; of Priestley, 230 ; 
Newton's work on, destroyed, 169 ; 
methods of studying, 397 ; recent ad- 
vances in organic, 408 

Chick, Harvey on development of 112 

23 



COSMOS 

Chinese, early science of, 4 ; mariner's 
compass known to the, 54 

Chladni on musical vibrations, 269 ; his 
musical sand figures, 273 

Chlorale, discovery of, 409 

Chloroform, discovery of, 409 

Chromosphere of the sun, 342 

Cinnamon tree, essences obtained from, 192 

Cipher, word derived from Arabic, 46 

Circulation of the blood, diagram of, 111 

Circular polarization in quartz crystals, 327 

Circumference of earth measured by Era- 
tosthenes, 27 

Classifications of plants, 69, 140, 207 ; of 
animals, 67, 140, 207, 433 

Clausen calculates the period of Biela's 
comet, 301 

Clausius on diffusions of gases, 363 

Clerk -Maxwell on molecular theory of 
gases, 363; on electro -magnetism, 364; 
on thermo-electricity, 378; on colour- 
blindness, 329 

Clifford, Mr., befriends Linnaeus, 206 

Climate, Humboldt on causes of, 424 ; 
Lamarck on effects of, 430 

Coal-tar, colours obtained from, 410 

Cod-fish, animalcules in roe of, 136 

Ccesium discovered, 338 

College of Surgeons, Hunter's collection in, 
198 

Colours, prismatic, 162 ; cause of, in tele- 
scopes, 166 ; caused by interference of 
light, 319 ; on the soap-bubble, 320; de- 
pend on light-vibrations, 177; theory of, 328 

Columbus, Christopher, his voyages, 56 ; 
discovers variation of magnetic needle, 57 

Columbus on circulation of the blood, 108 

Combustion, Hooke on, 128 ; Mayow on, 
129 ; Stahl's theory of, 133 ; cause of, 
proved by Lavoisier, 237 

Comet, Halley predicts return of, 159 

Comets, Newton on orbitsof, 151; returning, 
301 ; and meteors, 306 ; spectra of, 345 

Commutator of the Telegraph, 383 

Comparative anatomy, rise of, 197 ; Hun- 
ter's collection illustrating, 198 ; Halier 
on, 196 ; Cuvier on, 433 

Compass, figure of first mariner's, 54 

Compound flowers, 142 

Condenser, Watt's separate, 247 

Conservation of energy, 358 

Contraction of the muscles, 197 

Cook's voyage toobserve transit of Venus, 1 59 

Cooke patents electric telegraph, 382 

Copernican theory, 64 ; proofs of the truth 

of, 88 
Copernicus, life and work of, 63 
Cope, Professor, cited, 476 
Cordova, medical school of, 40 
Corpuscular theory of light, 174, 312 
Correlation of the physical forces, 476 

' Cosmos' of Humboldt, 423 



5°o 



INDEX. 



CRABTREE 

Crabtree sees transit of Venus, 154 

Critical point of gases, 406 

Crookes discovers thallium, 338 ; on ultra- 
gaseous state of matter, 365 ; on meta- 
elements, 405 

Crown of cups, Volta's, 260 

Crown-glass, dispersion of light in, 166 

Crystals, double refraction in, 179 ; pass- 
age of light-waves in, 326; circular 
polarization in quartz, 327 

Currents, from an electric battery, 261 ; 
Humboldt on ocean, 424 

Curtis, Dr., on carnivorous plants, 473 

Cuvier, history of, 427 ; on creation of 
animals, 431 ; on comparative anatomy, 
433 ; on fossil animals of Paris, 435 ; 
death of, 437 

Cycloidal pendulums, 175 

T^\ABURON, Ampere's visit to, 370 

■*-' Daguerre fixes sun-pictures, 332 

Dalton, life of, 399 ; law of multiple pro- 
portions, 401 ; atomic theory, 402 

Dark Ages, science of, 39 et seg. 

Darwin, 463 ; on origin of species, 464 ; on 
causes of natural selection, 467 

Daubenton's anatomical work, 204 

Davy, Sir H., his history, 390 ; his experi- 
ments on nitrous oxide, 391 ; on electro- 
lysis, 392 ; discovers potassium and 
sodium, 393 ; his safety lamp, 391 ; on 
sun-pictures, 331 ; melts ice by friction, 
352 ; cited, 409 

De Dominis on the rainbow, 161 

De la Rue cited, 343 

Delisle's method of measuring transit of 
Venus, 276 

Deltas, growth of, 12 

Democritus on the Milky Way, 15 

Denudation, Hutton on, 218 

Descartes on light, 104, 161 ; on the value 
of doubt, 103 

Development of animals, Lamarck on, 429 ; 
Von Baer on, 439 

Diagram showing how distances can be 
measured on the sun's face, 157 

Diagrams of bent and broken rocks, 216, 217 

Diameter of the sun, 158 

Diamond, nature of, proved by Lavoisier, 237 

Djafer, or Geber, Arabian alchemist, 43 

Diaecious plants explained by Caesalpinus, 70 

Dicotyledons, term explained, 141 

Differential calculus, by Leibnitz, 145 

Disc, Newton's rotating, 165 

Dispersion of light discovered by Newton, 
161 ; in different kinds of glass, 166 

Dissipation of Energy, 360 

Distillation known to Geber, 43, 
Distribution of animals, Buffon, 205 ; of 

plants, Humboldt on, 424 
Dogmatism of the sixteenth century, 64, 
78,81 



ENCKE 

Dollinger, anatomist, 438 

Dollond, Mr., makes achromatic telescope, 

166 _ 
Donati obtains spectrum of a comet, 345 
Dopier on movements of stars, 346 
Double refraction, 179 
Doubt, Descartes on the value of, 103 
Draper photographs a nebula, 347 
Drebbel makes alcohol thermometer, 118 
Ducts of plants, 137 
Du Faye on electricity, 253 
Dynamical theory of heat, 357 

T^ARL'S COURT, Hunter kept wild 

*—f animals at, 198 

Earth declared by Aristotle to be a globe, 
16 ; circumference of, measured, 28 ; 
Picart measures the size of the, 147 ; 
Newton on shape of the, 151 ; measure- 
ment of density of the, 287 

Eurth-light on the moon, 88 

Earthquakes, Pythagoras on, 12 ; Strabo 
on causes of, 33 ; changes of level caused 
by, 445 

Ebn Junis, Arabian astronomer, 45 

Eclipses explained by Anaxagoras, 13 

Ecliptic or sun's path, hew traced out by 
the Greeks, 18 ; Anaxagoras discovers 
obliquity of, 21 

Egyptians, early science of, 4 

Eighteenth century, work of the, 478 ; 
summary of science of, 289 

Elective affinities, Bergmann on, 227 

Electric currents causing magnetic field, 
371; making electro - magnets, 372; 
power of, to conquer chemical affinity, 392 

Electrical machines, Guericke's, i2r ; 
Hawksbee's, 121 

Electric spark observed by Guericke, 122 

Electric telegraph, invention of, 382; 
Bain's set on fire by magnetic storm, 
381 ; Morse's and Steinheil's, 383 ; 
Bain's and Cowper's, 386 

Electricity, Gilbert on, 74, 121 ; attraction 
and repulsion by, 122 ; Du Faye on dif- 
ferent kinds of, 253 ; Franklin on, 254 ; 
and lightning, 255 ; animal, 257 ; chemi- 
cal or voltaic, 259 ; chemical theory of, 
394 ; produced by heat, 377 

Electrolysis, discovery of, 392 

Electro - magnetism, Oersted discovers, 
367 ; Ampere on, 370 ; Faraday on, 374 

Electro-magnets made by electric current, 
37 2 

1 Electron,' root of word ' electricity,' 75 

Elements, chemical, 398 ; dissociation of, 
405 

Ellipses, planets move in, 96 

Embryology, Von Baer's law of, 437 

Embryos of animals alike in structure, 42 

Emission theory of light, 174, 316 

Encke's comet, 300 



INDEX. 



501 



ENERGY 
Energy, potential and active, 357 ; con- 
servation of, 358 ; dissipation of, 360 
Engines, history of, 244 ; the Newcomen, 

245 ; Watt's double-acting, 249 
England, geological map of, by W. Smith, 

222 
Epicycles, theory of, 64 
Epidermis studied by Malpighi, 136 
Equinoxes observed by Thales, 9 ; Hip- 

parchus discovers precession of, 30 
Erasistratus on the brain, 26 
Erratic blocks, on the Jura, 450 ; a proof 

of former extension of ice, 451 
Eratosthenes lays down first parallel of 

latitude, 27 ; measures circumference of 

the earth, 28 
Ether, light a vibration of the, 176 
Euclid, some problems of, invented by 

Thales, 9 
Euclid discovers that light travels in 

straight lines, 21 
Eudoxus explains movements of the 

planets, 15 
Euler on sound, 263 
Eustachius the anatomist, 66 
Evolution, theory of, 457 
Extinct animals restored by Cuvier, 435 ; 

man contemporary with, 452 
Eye, Alhazen on the sight of the, 46 ; Porta 

on structure of the, 74 ; Kepler on the, 94 

FABRIC1US Aquapendente discovers 
valves in veins, 109 

Fahrenheit thermometer, freezing-point 
of, 118 

Falling bodies, Galileo on rate of, 78 

Fallopius, the anatomist, 66 

Faraday, history of, 373 ; on rotation of 
magnets and electric wires, 374; on 
electric current produced by a magnet, 
376 ; on connection between electricity 
and chemical changes, 394 ; on liquefac- 
tion of gases, 406 ; discovered benzole, 410 

Faust, John, the printer, 55 

Fire -air discovered by Mayow, 129 ; its 
effect on the blood, 132 

' Fixed air,' Black on, 225 ; Bergmann 
tests, 227 

Fizeau on velocity of light, 327 

Flame, spectra of different kinds of, 336 

Flamsteed, 84, 153, 282 

Flint implements of Abbeville, 453 

Flint-glass, dispersion of light in, 166 

Flood, attempt to explain fossils by a uni- 
versal, 214 

Fluxions, Newton's method of, 145, 150 

Forces, convertibility of, 397 ; of gravita- 
tion, 146 

Fossil animals restored by Cuvier, 435 ; 
intermediate forms of, 460 ; found in 
Rocky Mountains, 476 

Fossil shells observed by Pythagoras, 11 



GERANIUM 

Fossils, Gesner on, 68 ; first attempts to 
explain, 214 ; used by W. Smith for 
classification, 222 

Foucault on velocity of light, 327 

Frankland, Dr., cited, 410 

Franklin's early life, 252 ; he proves light- 
ning to be electricity, 255 

Fraunhofer's early life, 334 ; lines, 335 

French school of chemistry, 238 

Fr^snel, history of, 324, on polarization of 
light, 324 ; on circular polarization, 327 

Freyberg, Werner's lectures at, 216 

Friction, ice melted and water boiled by, 

35 2 
Friendship of Ray and Willughby, 139 
Frog's leg, electricity in, 259 
Fust, J. See Faust 

GALEN, physiology of, 34 ; corrected 
by Vesalius, 65 
Galileo on the pendulum and on falling 
bodies, 77 ; on musical notes, 80 ; on 
secondary light of the moon, 87 ; on 
Jupiter's moons, 88 ; on phases of Venus, 
89 ; on sun-spots and rotation of sun on 
its axis, 90 ; demonstrates the truth of 
Copernican theory, 89, 92 ; his telescope, 
87 ; his recantation, 91 ; on rising of 
water in a pump, 114; makes a water 
thermometer, 118; compared with Tycho 
and Kepler, 100 
Galle finds Neptune, 304 
Gallium discovered, 338 
Galvani on animal electricity, 257 ; his 

controversy with Volta, 259 
Galvanism, 258 

Galvanometer invented by Ampere, 377 
Ganges, mud carried down by the, 444 
'Gas,' term used by Van Helmont, 71; 

Nebulae composed of, 344 
Gases, Boyle's law of, 126 ; Bacon on, 52 ; 
Mayow on, 129 ; discovery of the four 
important, 225 ; spectra of, 337 ; atmo- 
sphere of, round the sun, 341 ; diffusion 
of, 363 ; critical point of, 406 ; liquefac- 
tion of, 406 ; molecular theory of, 362 
Gassendi observes transit of Mercury, 154 
Gauss re-discovers Ceres, 299 
Gay-Lussac on multiple volumes, 404 
Geber the founder of chemistry, 43-45 
Geddes, Mr., on embryonic development, 

440 
Geist, word ' gas' derived from, 71 
Geography, Ptolemy's work on, 33 ; Strabo 

on, 33 

Geology, definition of, 2 ; of Pythagoras, 

it; neglected in Dark Ages, 213 ; Lazzaro 

Moro on, 215 ; Werner on, 216 ; Hutton 

on, 218 ; W. Smith on, 221 ; Sir C. Lyell 

on, 442; prejudices retarding, 441 

George II. founds Gottingen University, 195 

Geranium, Linnasus's definition of the. 208 



502 



INDEX. 



GERBERT 

Gerbert introduces Arabic numerals into 
Europe, 46 

Germany, Imperial Academy in, 124 

Gesner, his cabinet and garden, 67 ; his 
history of animals, 67 ; his botanical 
classification, 68 

Gilbert, first experiments on electricity, 74 

Gioja discovers mariner's compass, 53 

Glacial period, 448 

Glacier, illustration of a, 449 ; carrying 
blocks to the Jura, 450 

Gladstone, Dr., his life of Faraday, 374 

Glass, angle of polarization of light from, 
323 ; index of refraction for, 106 ; dif- 
ferent dispersive powers of, 166 

Glasses, musical, 272 

Glen Tilt, granite veins in, 221 

Gnomon at Alexandria, 28 

Goethe on metamorphosis of plants, 414 ; 
on discussion between Cuvier and St. 
Hilaire, 432 

Gold separated from amalgam by Paracel- 
sus, 70 

Gottingen University founded, 195 

Graebe cited, 410 

Graham, Dr., on diffusion of gases, 363 

Graham on variations of magnetic needle, 
380 

Granite, Hutton on formation of, 220 ; 
veins in Glen Tilt, 220 

Gravitation, law of, explained, 145-150 ; 
discovered by Newton, 147 ; its action 
on the planets, 149 ; decreases with the 
square of the distance, 150 ; problems 
explained by, 151 ; holding distant stars 
together, 284 

Graecus, Marcus, discovers gunpowder, 42 

Gratz, Kepler professor at, 93 

Greece, Roman conquest of, 35 

Greek colonies in Ionia, 8 

Greeks deficient in natural knowledge, 8 ; 
believed the sun moved round the earth, 
19 ; knew electric nature of amber, 75 ; 
general remarks on science of the, 35 

Grew on vegetable anatomy, 137 ; on 
stomates, 138 

Grove cited, 479 

Guericke's air-pump, 119; Magdeburg 
hemispheres, 120 ; first electrical ma- 
chine, 122 ; his experiments on electri- 
city, 123 

Gunpowder known to the Arabs, 42 

Gutenberg, John, the printer, 55 

HALES, Dr., on gases, 225; on water 
in plants, 193 
Hall, Asaph, on satellites of Mars, 311 
Hall, Mr. C. More, on flint and crown 

glass, 166 
Hall, Sir J., on melted rocks, 220 
Halle, Dr., pleads for Lavoisier's life, 238 



HUGGINS 

Haller, early life of, 195 ; on contraction of 
the muscles, 196 ; on comparative ana- 
tomy, 196 

Halley, his method of measuring transits, 
155 ; observes transit of Mercury, 155 ; 
predicts the return of a comet, 159 

Harding discovers Juno, 300 

Harvey discovers circulation of the blood, 
108 ; on development of the chick, 112 

Hawksbee's electrical machine, 121 

Heat, Bacon's examination of, 102 ; early 
theories about, 349 ; produced by friction, 
350 ; latent, 240, 353 ; Joule's experi- 
ments on, mechanical equivalent of, 
354 ; converted into motion, 358 ; pro- 
duction of electricity by, 378 

Heat-rays discovered, 330 

Heavy bodies, Galileo on motions of, 79 

Helmholtz cited, 363 ; on conservation of 
energy, 360 ; theory of colour, 328 

Henry brothers photograph an unseen 
nebula, 347 

Hercules, motions of our solar system to- 
wards, 285 

Hermes and hermetic philosophers, 41 

Hero's engine, 244 

Herophilus on muscles, nerves, and the 
pulse, 26 

Herschel, Sir W., 281 ; discovers Uranus 
and receives a pension, 283 ; on binary 
stars, 283 ; on nebulae, 284 ; on motion of 
solar system through space, 285 ; dis- 
covers heat-rays, 330 ; on cause of sun- 
spots : 379 

Herschel, Sir J., work in astronomy, 305 ; 
on spectrum analysis, 336 

Herschel, Miss C., her brother's assistant, 
286 

Herschel, Mr. A., on spectrum of falling 
stars, 345 

Hiero's crown, Archimedes on, 22 

Higgins on chemical law of proportions, 400 

Hipparchus, astronomy of, 29 ; discovers 
precession of equinoxes, 30 

Hippocrates the father of medicine, 14 

Him, M., his experiments on heat con- 
verted into motion, 358 

Hodgson, M., on outbreak on a sun-spot, 381 

Hoffmann, Dr., cited, 410 

Homology, St. Hilaire on, 432 

Hooke, one of the founders of the Royal 
Society, 123 ; on air-pump, 126 ; on com- 
bustion, 128 ; on geology, 215 

Hooker, Sir W., on botany, 421 

Horrocks observes transit of Venus, 154 

Horse, ancestors of the, 462, 476 

Huen island, Tycho's observatory on, 76 

Huggins, Dr., on spectrum analysis of the 
stars, 343 ; of nebulae, 344 ; measured 
movement of Sirius, 346; on spectrum of 
a comet, 345 



INDEX. 



5o3 



HUMAN 

Human anatomy, Vesalius on, 65 

Humboldt, 423 ; on isothermal lines, 424 ; 
his 'Cosmos,' 423; on meteors, 307 ; pays 
expenses of AgassiVs work, 447 

Hunter, John, his birth and history, 197 ; 
on comparative anatomy, 198 ; his mu- 
seum, 199 

Hutton on geology, 218 ; on granite veins, 
221 ; on size and weight of Schehallion, 
289 

Huyghens, 134; history of, 174; invents 
cycloidal pendulum and describes 
Saturn's ring, 175 ; his undulatory 
theory of light explained, 175 ; on re- 
fraction of light, 177 ; on double refrac- 
tion, 179 

Huxley on fossil bird-reptile, 462 ; on rapid 
multiplication of plants, 467 ; cited, 475 

Hydrogen discovered by Cavendish, 229 ; 
name given by Lavoisier, 238 ; amount 
of, in water, 400 ; size of molecules of, 
364 ; liquefaction and solidification of, 407 



ICE, heat lost in melting, 241 ; melted by 
friction, 352 ; rocks scratched and 

blocks carried by, 449 
Iceland spar, double refraction in, 179 
Igneous rocks, Hutton on, 220 
Imperial Academy of Germany founded, 

124 
Index of refraction, 107 
Indians, early science of, 4 
Indium discovered, 338 
Induction-coil, 377 
Inquisition banishes Vesalius, 66 ; burns 

G. Bruno, 81 ; forces Galileo to recant, 

91 
Insects, Ray's work on, 141 ; microscopic 

anatomy of, 136 ; fertilisation of plants 

by, 415, 467, 472 
Interference of light, 319 ; colours caused 

by, 320 
Invertebrate animals, Lamarck on, 428 
Ionian school of learning, 8 
Iron tools of lake-dwellings, 454 
Islands, formation of, 11 
Isothermal lines, Humboldt on, 424 
Italy, early scientific societies in, 124 



JAMES, Sir H., on weight of the earth, 
289 
Jpnsen makes a telescope, 85 
Janssen on photosphere of the sun, 342 
Jews, medical knowledge of the, 40 
Joule, Dr., experiments on the mechanical 

equivalent of heat, 355 ; cited, 363 
Juno discovered, 300 
Jupiter, atmosphere of, 344; his moons, 

88 *, velocity of light measured by, 172 ; 

and Saturn, long inequality of, 279 



LIBRATION 

Jura mountains, erratics of the, 450 
Jussieu's natural system of plants, 209, 
412 

TRENT'S Hole, flint implements found 

rS ' in, 453 

Kepler, life of, 93 ; on structure of eye, 
94 ; his telescope, 95 ; his first law, 
95 ; second law, 97 ; third law, 98 ; his 
delight at Galileo's discoveries, 98 ; pre- 
dicted transits of Mercury and Venus 
154 ; finished Rudolphine tables, 99 

Kerner on fertilisation of plants, 472 

Kircher invents magic lantern, 74 

Kirchhoff on dark lines in solar spectrum, 
338 ; his spectroscope, 339 

Kite, Franklin's, 256 

Koran iorbade dissection, 40 

LACTEALS discovered by Asellius, 
112 

Lagrange, 276 ; on libration of the moon, 
277 ; on stability of planetary orbits, 280 

Lake-dwellings of Switzerland, 453 

Lamarck, 426 ; on invertebrates, 428 ; on 
development of animals, 429 ; weak 
point in his theory, 430 

Lamont on variations of magnetic needle, 

3 8 ° . • , . 

Land, conversion of, into sea, 10 
Laplace, 277 ; on long inequality of Jupiter 

and Saturn, 280; on moon's acceleration, 

280 
Lassell on Neptune's moon, 304 
Latent heat, Black on, 240 ; theory of, 

applied by Watt, 243 ; explained, 353 
Latitude, first parallel of, laid down, 27 
Laughing-gas, Davy's experiments with, 

39 1 
Lavoisier the founder of modern chemistry, 
234 ; his experiments, 236 ; his death, 

Law of compressibility of gases, 126 ; of 
definite proportions in chemistry, 399 ; 
of multiple volumes, 405 ; of gravitation, 
148 ; of refraction discovered by Snellius, 
104 
Laws of Kepler, 95 et seq. 
Leaves of plants, Bonnet on use of, 200 
Leeuwenhceck on animalcules, 136 
Leibnitz on differential calculus, 145 
Leidy, Dr., on fossil animals, 476 
Lenses, Alhagen on use of, 48 ; Porta on, 

74 ; Galileo on, 86 ; Kepler on, 94 
Lescarbault's supposed planet, 312 
Leslie, Sir J., on refraction of heat, 359 
Lever, Archimedes on the, 22 
Leverrier calculates the position of Nep- 
tune, 302 ; on November meteors, 309 ; 
his analysis of planetary orbits, 312 
Leyden, medical school of, 190 
I Libration of the moon, 277 



5°4 



INDEX. 



LIEBIG 

Liebig on organic chemistry, 408 
Light, Euclid on rays of, 21 ; a vibration, 
175 ; causing colour, 177 ; polarization 
of, 180, 322 ; compared to sound, 175 ; 
dispersion of, 161 ; blending of colours 
into white, 165 ; interference of, 319 ; 
undulations compared to waves of a pond, 
319 ; reflection of, from a soap-bubble, 
321; complex vibrations of, 326; passage 
of, through a crystal, 326 ; Roemer 
measures velocity of, 172 ; theories of, 
173 ; undulatory theory explained, 175 ; 
Fizeau and Foucault on velocity of, 327 
Lightning, electric nature of, proved by 

Franklin, 255 ; conductors, 257 
Lilienthal, meeting of astronomers at, 200 
Limestone, fixed air obtained from, 225 ; 

beds of Sicily, thickness of, 443 
Lines in the spectrum, 336 
Linnaean system, 207 ; collection brought 

to England, 211 
Linnaeus, early life of, 205 ; his ' Excur- 
sions,' 207 ; gives specific names to plants 
and animals, 207 ; death and character 
of, 211 
Lippershey makes a telescope, 85 
Liquefaction of permanent gases, 406 
Lithuanian legend about falling stars, 307 
Lizards, unpaired rudimentary eye in, 475 
Loadstone known to the Greeks, 53 
Locke on heat, 349 

Lockyer on spectrum of the sun's atmo- 
sphere, 342 ; on dissociation of elements, 
405 
Locomotive-engine, date of first, 244 
Loewy cited, 343 

Looking-glass, cause of reflection of, 177 
Loschmidt on size of molecules, 364 
Lungs, circulation of blood through the, 

in ; studied by Malpighi, 135 
Luxembourg Palace, polarized light re- 
flected from windows of, 323 
Lyell, Sir C, his history, 442 ; on present 
causes of geological change, 442-445 ; on 
Darwin, 464 
Lymphatics discovered by Riidbeck, 113 



MCENERY on flint implements of 
Kent's Hole, 4 53 

Magdeburg hemispheres, 120 

Magellan's ship sails round the world, 57 

Magellanic clouds, 306 

' Magia Naturalis ' published, 72 

Magic lantern invented, 74 

Magnet, origin of name, 53 ; producing 
electric current, 376 ; and electric wires, 
mutual rotation of, 374 

Magnetic field caused by electric currents, 
371 ; needle, direction of, 369, 380 ; varia- 
tions of the, 57 ; Ampere on direction of, 
371 ; sudden movement of, at Kew, 381 



MILLER 

Magnetism, Gilbert on, 75 4 electro-, 372 ; 
terrestrial, affected by sun-spots, 379" 

Magnifying glasses explained, 49 

Malpighi applies the microscope to living 
structures, 134 ; discovers Malpighian 
layer, 136 ; on silkworm, 136 ; on struc- 
ture of plants, 137 

Malus on polarization of light, 322 

Man, antiquity of, 452 ; selection of ani- 
mals by, 466 

Map made by Anaximander, 10 ; geologi- 
cal, made by W. Smith, 222 

Marcus Grsecus, gunpowder made by, 42 

Mariner's compass, 54 

Marquis of Worcester's engine, 244 

Mariotte's law, 128 

Mars, atmosphere of, 344 ; movements of, 
explained by Kepler, 95 ; occultation of, 
observed by Aristotle, 15 ; discovery of 
satellites of, 311 

Marsh, Professor, on fossils of Rocky 
Mountains, 476 

Maskelyne measures the destiny of the 
earth, 288 

Matter, ultra-gaseous state of, 365 

Maury on division of Biela's comet, 301 

Maxwell. See Clerk-Maxwell 

Mayer, Dr., on mechanical equivalent of 
heat, 355 

Mayow discovers 'fire-air,' 130; his ex- 
periments on combustion and respiration, 
129 

' Mecanique Celeste' of Laplace, 281 

Mechanical equivalent of heat, 355 

Mechanics, definition of, 2 

Medical school of Le} r den, 191 

Medicine, Hippocrates the iather of, 14 ; 
Galen on, 34 

Medusa?, nervous system of the, 475 

Melloni on passage of heat rays, 359 

Mercurial thermometer, how made, 118 

Mercuric oxide, Priestley obtains oxygen 
from, 231 

Mercury obtained from cinnabar by Geber, 
44 ; sustained in a tube by weight of air, 
116 ; combining with oxygen, 236 

Mercury, transits of, observed, 154; planets 
within the orbit of, 312 

Meta-elements, Crookes on, 405 

Metals, Geber notices increased weight of 
heated, 44 ; electric discharge from two, 
260 ; discovered by spectrum analysis, 
338 

Metamorphosis of plants, 414 

Meteors and their paths, 306 ; their com- 
position, 307 ; spectrum analysis of, 345 

Microscope applied to living structures, 134 

Middle Ages, science of the, 39-59 

Milky Way studied by Democritus, 15 ; 
by Galileo, 88 

Miller, Dr., on spectrum analysis of the 
stars, 343 



INDEX. 



505 



MINERAL 

Mineral waters analysed by Bergmann, 227 
Mineralogy, Gesner on, 68 ; Werner's 

lectures on, 216 
Mirbel on ovules, 418 
Mohl, H. von, on protoplasm, 420 
Moldenhauer cited, 417 
Molecular theory of gases, 362 
Molecules, size of, 364 ; vibration of, 364 ; 

ultra-gaseous state of, 365 
Monochord invented by Pythagoras, 12 
Monocotyledons, term explained, 142 
Monro cited, 411 
Mont Blanc, erratic blocks carried from, 

450 
Moon, Anaxagoras on the, 13 ; phases of, 
explained by Anaximander, 10 ; Thales 
on reflection of the, 9 ; secondary light 
of the, 87 ; movement of, used by New- 
ton to test his law of gravitation, 146 ; 
Lagrange on libration of, 277 ; why she 
turns the same face to us, 278 ; photo- 
graphs of the, 347 
Moons, Jupiter's, 88 
Moraines of glaciers, 448 
Moro, Lazzaro, on formation of strata, 215 
Morse, his electric telegraph, 383 
Mountain-chains, Eratosthenes studies, 29 
Mouse consuming air in a bell-jar, 132 
Mud carried down by the Ganges, 444 
Midler, Dr. H., on plants and insects, 415, 

472 
Murchison cited, 446 

Muscles, Haller on contraction of the, 197 
Musical notes, Pythagoras on, 12; Galileo 
on, 80 ; Sauveur on number of vibrations 
in, 265 ; sand figures formed by, 273 

NAMUR, human skeletons of, 455 
Napoleon I. takes St. Hilaire to 
Egypt, 428 
Natural history of seventeenth century, 138 
Natural philosophy, Leonardo da Vinci 

on, 58 
Natural selection, theory of, 464 ; diffi- 
culties of natural history explained by, 
469 ; does not exclude Divine Power, 470 
Natural system of plants, 209, 412 
Nebulae, Herschel on the nature of, 284 ; 

spectrum analysis of, 344 
Nebular hypothesis, 281 
Negative and positive electricity, 255, 261 
Negro, colouring matter in skin of, 135 
Neptune, position of, found by Adams and 
Leverrier, 302 ; seen by Galle, 304 ; his 
moon, 305 
Neptunists and Vidcanists, 3,17 
Nerves, Galen on two sets of, 34 
N estorians, science of the, 40 
Neuchatel, erratic block near, 450 
Newcomen's engine, 244 
Newt, regrowth of eye of, 201 



OXYGEN 

Newton, birth and early life of, 144 ; his 
law of gravitation, 145 ; his method of 
fluxions, 145 ; on variation of attraction, 
150; on cause of tides, 152; on specific 
gravity of planets, 152 ; on shape of the 
earth, 152 ; on precession of equinoxes, 
152; on motion of comets, 152; on 
sound, 166 ; on chemical attraction, 228 ; 
on attraction of plumbline to a moun- 
tain, 287 ; on dispersion of light, 161 ; 
explains the spectrum, 162 ; his rotating 
disc, 165 ; his work on, chemistry de- 
stroyed, 170 ; his work on optics, 166 ; 
his theory of light, 173 ; on nature of 
sound, 366 

Newton, Professor, on meteors, 309 

Nicholson on decomposition of water by 
electricity, 392 

Nile, mud carried down by, n 

Nineteenth century, tendency of science 
of, 478 

Nitrogen, compounds of oxygen with, 401 ; 
Rutherford on, 234 ; liquefaction of, 407 

Nitrous oxide, Davy's experiments on, 391 

Nobili on animal electricity, 259 

Noble on stretched strings, 563 

Nodes in musical strings, 267 

' Novum Organum,' 101 

Numerals, Indian, introduced into Europe 
46 

Nutation of earth's axis, 275 



QBLIQUITY 
^-^ on, 21 



of ecliptic, Anaxagoras 



Observatory, Tycho's, 76 

Oersted on electro-magnetism, 367, 382 

Olbers, Dr., discovers Pallas and Vesta, 
300 

Optics, Alhazen on, 46 ; Porta on, 72 ; 
Kepler on, 9* ; Newton's work on, 166 ; 
' Opus Majus' of Roger Bacon, 51 

Orbits of the planets, elliptical, 96 ; go- 
verned by gravitation, 149 

Organic compounds, chemistry of, 190 ; 
Liebig on, 408 ; recent advances in, 409 

Organs of digestion arranged by Hunter, 
199 ; Lamarck on modification of, 430 ; St. 
Hilaire on modification of, 431 

Origin of species, 464 

Orion, nebula of, photographed, 347 

'Ossemens Fossiles' published, 436 

Ovid's 'Metamorphoses,' n 

Oviparous and viviparous animals, 140 

Owen on classification, 475 

Oxford, early meetings of Royal Society 
at, 123 

Oxygen called 'fire-air' by Mayow, 130; 
discovered by Priestley and Scheele, 
230 ; amount of, in water, 400 ; com- 
pounds of, with nitrogen, 401 ; liquefac- 
tion of, 407 



qo6 



INDEX. 



PALISSY 

UALISSY on fossil shells, 214 

-L Pallas discovered, 300 

Palaeontology, growth of, 476 

Papin's engine, 245 

Parabolas described by comets, 150 

Paracelsus, chemistry of, 70 

Paris, Cuvier on fossil animals of, 435 

Parker, W. Kitchen, on structural links in 

the vertebrate kingdom, 440 
Pascal on pressure of the atmosphere, 117 
Pecquet on thoracic duct, 112 
Peltier cited, 378 

Pericles pleads for Anaxagoras, 14 
Perkins, Mr., discoverer of aniline dyes, 410 
Perrier M., carries a barometer up the 

Puy de Dome, 117 
Pendulum, Galileo on the, 77 
Petrology, study of, 455 
Phases of moon, 10 ; of Venus, 89 
Philosopher, name first given to Pytha- 
goras, 12 
Philosophical transactions begun, 124 
Phlogiston, theory of, 132 ; destroyed by 

Lavoisier, 237 
Photography explained, 332 ; used in as- 
tronomy, 347 
Photosphere of the sun, 343 
Physical forces, correlation of the, 479 ; 

geography, Humboldt on, 424 
Physics, definition of, 2 ; of sixteenth cen- 
tury, 80; of seventeenth century, 184; of 
eighteenth century, 292 
Physiology, beginning of the study of, 108 
Piazzi discovers Ceres, 299 
Picart, size of the earth measured by, 147 
Pickering on size of satellites of Mars, 311 
Pictet liquefies permanent gases, 407 
Pierre-a-Bot, an erratic block, 450 
Pigeons, common descent of different varie- 
ties of, 466 
Pigot on stretched strings, 263 
Pisa, Galileo and the men of, 78 
Pith of elder, cells in, 137 ; ball attracted 
and repelled by rubbed sealing-wax, 122 
Planets. Anaxagoras on, 14 ; Euxodus on, 
15 ; Kepler's laws concerning the, 95-99 ; 
held in their orbits by gravitation, 149 ; 
minor, or asteroids, 299 ; stability of 
their orbits proved by Lagrange, 280 ; 
analysis of their orbits by Leverrier, 
312 ; intermercurial, 312 
Plants, Aristotle on low organisation of, 
16 ; Theophrastus on, 17 ; microscopic 
structure of, 137 ; ashes of, examined by 
Boerhaave, ig2 ; Hales on breathing of, 
193 ; Bonnet on leaves of, 200 ; Gesner 
on, 68 ; Csssalpinus on, 69 ; Ray on, 141 ; 
Linnaeus, artificial system of, 209 ; Jus- 
sieu, natural system of, 209, 412 ; speci- 
fic names given to, 208 ; Humboldt on 
distribution of, 424; metamorphosis of, 
414 ; Priestley on breathing of, 231 ; 



RAYS 

fertilisation by insects, 415, 467, 472 ; 

colouring matter in, 410 ; carnivorous, 

472 
Plates, vibrations of musical, 273 
Playfair's illustrations of Hutton, 218 
Pleiades, nebula discovered in the, 347 
Pliny the naturalist, 33 
Polarization of light, 180; by reflection, 

322 ; circular, 327 
Porta, his meetings in Naples, 72 ; his 

camera obscura, 73 ; on the eye, 74 ; his 

engine, 244 
Positive and negative electricity, 255 
Potassium discovered by Davy, 393 
Potter, Humphrey, ties the engine-cocks, 246 
Precession of equinoxes discovered by 

Hipparchus, 30 ; Newton on, 151 
Pressure and volume, relations of, 128 
Prestwich on flint implements, 453 
Priestley, his discoveries, 230-233 
Prism, light dispersed in a, 162 
Prismatic colours, Newton on, 164 
' Principia,' some problems discussed in 

the, 151 
' Principles of Geology ' published, 446 
Printing, invention of, 55 
Proctor on shooting stars, 309 
Proportions, law of definite, 400 
Protoplasm explained, 420 
Proust on chemical law of proportions, 400 
Ptolemaic system, 32 
Ptolemies patrons of learning, 18 
Ptolemy, astronomy of, 32 ; geography of, 

33; ' cloudy stars ' seen by, 284 
Pulmonary circulation of the blood, 11 1 
Pulse studied by Herophilus, 27 
Pump, height that water will rise in, 114 
Pythagoras, science of, 11, 213 ; his mono- 
chord, 12 
Pythagorean system, 21 

(QUADRANT made by Copernicus, 64 
\zj Quadrupeds, Ray's work on, 140 
Quicklime, nature of, 225 

RABBITS descended from one wild 
stock, 430 

Radiometer, 365 

Rain, denuding effects of, 442 

Rainbow, De Dominis on, 161 

Ramsay, Professor, cited, 217 

Ray and Willughby, history of, 139; on 
quadrupeds, 140 ; on birds, fishes, and in- 
sects, 141 ; on plants, 141 ; on geology, 215 

Rays of light, index of refraction of, 107 ; 
Euclid on, 21 ; Alhazen on refraction of, 
47 ; Kepler on, 94 ; Young and Fresnel 
on, 326 ; Newton on refraction of co- 
loured, 162 ; non-interference of ordinary 
and extraordinary, 325 ; paths of through 
a crystal, 326 ; discovery of chemical and 
heat, 330-331 



INDEX. 



507 



REAUMUR 
Reaumur's scale, freezing point of, 118 
Red fire made by burning strontium, 337 
Red prominences of the sun, 342 
Reflection of light, 176 ; polarization of 

light by, 322 
Refraction explained by Alhazen, 47 ; ex- 
plained Huyghens, 177 ; figures illus- 
trating, [178 ; double, 179 ; Snellius dis- 
covers law of, 104 ; method of measuring, 
105 ; of coloured rays, 161 
' Regne Animal,' Cuvier's, 433 
Reptiles, gigantic fossil, 460, 476 
Repulsion by electricity, 122 
Respighi on height of red prominences, 343 
Respiration, Boyle on air used in, 128; 

Mayow on effects of fire-air in, 129 
Richter on chemical law of proportions, 

400 ; and Reich discover indium, 338 
Rieban, Faraday's master, 373 
Ritter discovers chemical rays, 331 
Rivinus on plants, 208 
Robison on Watts, 244 
Rocks, diagrams of, bent and broken, 216 ; 

new ones formed out of old, 219 
Rocky Mountains, fossils of the, 476 
Roe of codfish, animalcules in, 136 
Roemer measures velocity of light, 172 
Roger Bacon makes gunpowder, 52 ; his 

experiments on air, 52 
Romanes on nervous system of Medusae, 475 
Ronald's, Mr., attempt at electric tele- 
graph, 382 
Rose, modification of parts in the, 414; 

number of species of, 438 
Rothmann, Dr., befriends Linnaeus, 205, 206 
Royal Institution, Young professor at, 316 ; 

Davy at, 391 ; Faraday at, 374 
Royal Society founded, 123 ; early mem- 
bers of, 125 ; Newton learns the real 
size of the earth at the, 147 
Rubidium discovered, 338 
Riidbeck discovers lymphatics, 113 
Rudimentary organs, 459 
Rudolph II. protects Tycho and Kepler, 

76, 93 
Rudolphme tables, 93 ; used to predict 

transits, 154 
Rumford, Count, produces heat by friction, 
350; appoints Davy to Royal Institution, 
39i 
Rutherford, Dr., on nitrogen, 234 
Rutherford, Mr., his moon photographs, 347 



C ABINE, Sir E., on connection between 
S - J sun-spots and magnetic currents, 379 ; 

on weight of our earth, 289 
Sachs, Professor, cited, 472 
St. Hilaire, G., 412 ; on Egyptian animals, 

428 ; on homologous parts of animals, 431 
Salamanders, re-growth of limbs of, 201 
Sal-ammoniac known to the Arabs, 45 



SMITH 

Salerno, medical school of, 40 

Salt, colour of burning, 337 

Salts of plants extracted, 193 

Sand-figures, musical, 273 

Sanderson, Dr. Burdon, on carnivorous 
plants, 473 

Sap, Ray and Willughby on, 140 

Satellites of Jupiter, 88; eclipses of, 172 

Satellites of Mars, 311 

Saturn, atmosphere of, 344 ; weight of, 151 ; 
his ring seen by Galileo, go ; and Jupiter, 
long inequality of, 279 

Saussure, De, on glaciers, 449 

Sauveur on musical sound, 263 

Savery's engine, 245 

Scheele, discoveries of, 230 ; on chemical 
rays of light, 331 

Schehallion experiment, diagram of, 288 

Schiaparelli on August meteors, 308 

Schimper cited, 474 

Schoeffer, Peter, the printer, 55 

Schwabe on periodicity of sun-spots, 379 

Science, definition of, 1 ; of the Greeks, 7 : 
decay of Greek, 35 ; of the Middle Ages, 
39, 59 ; of the Arabs, 39 ; rise of modern, 
61 et seq. ; of sixteenth century, 80 ; 
seventeenth century, _ 182 ; eighteenth 
century, 289; academies of, 122 

Scilla on Calabrian fossils, 214 

Scotland, glaciation of, 451 

Screw of Archimedes, 25 

Sea, land eaten away by the, 444 

Seasons caused by obliquity of ecliptic, 20 

Section of the skin, 136 

Sedgwick cited, 446 

Seebeck, Professor, discovers thermo-elec- 
tricity, 378 

Seeds and eggs, growth of, compared, 138 ; 
classification of plants by, 69 ; Robert 
Brown on structure of, 419 

Segments in musical strings, 267 

Seguin, M., on mechanical equivalent of 
heat, 355 

Selection of animals by man, 466 ; natural, 
466 _ 

Serapis, rise and sinking of temple of, 445 

Servetus on circulation of blood, 108 

Seventeenth century, characteristic work 
of, 478 ; summary of science of the, 182 

Shooting-stars, a legend concerning, 307 

Sicily, thickness of limestone rocks in, 443 

Silkworm, Malpighi on structure of, 136 

Simpson, Dr., on chloroform, 409 

Sines of incident and refracted rays, 106 

Sirius, movements of, 346 

Sixteenth century, advance of science in 

the, 80, 478 
Skaptar Jokul, torrent of lava from, 445 
Skin, section of, 136 

Slough, Herschel's observatory at. 283, 305 
Smith, Sir E., brings Linnaean collection to 
England, 211 



508 



INDEX, 



SMITH 

Smith, William, surveys England, 221 

Snails, regrowth of parts in, 201 

Snellius discovers law of refraction, 104 

Soap-bubble, Newton, on the, 166 ; cause 
of colours on the, 320 

Soda, composition of, 403 

Sodium discovered by Davy, 393 ; power 
of, to decompose water, 403 ; spectrum 
of, 337 ; Kirchhoff's experiments with 
vapour of, 340 

Soho, manufactory of engines at, 250 

Soil, substances taken from, by plants, 
193 

Solar spectrum, dark lines in, 338 ; system, 
motion of through space, 285 

Solstices observed by Thales, 9 

Sound, Newton on, 166 ; light compared 
to, 175 ; Pythagoras on, 12 ; Galileo on 
musical, 80 ; Newton on transmission of, 
166 ; Sauveur and Chladni on musical, 
263-274 

Spallanzani on regrowth of severed limbs, 
201 

Specific gravity first measured by Archi- 
medes, 23 

Specific names given by Linnaeus, 207 

Spectra, table of, 335 

Spectroscope, movement of stars studied 

by, 346 

Spectrum studied by Newton, 162 ; dark 

lines on the, 338 ; their cause explained, 

340; of gases and solids, 337 
Spectrum analysis, history of, 333 - 347 ; 

metals discovered by, 338 ; of sunlight, 

339 ; of stars, of comets, and nebulas, 344 ; 

of meteors, 345 ; use of, in chemistry, 

398 
Spencer, Herbert, on evolution, 479 
Spirit, Arabian name for gas, 42 
Spirits of wine made by Geber, 44 
Spots on the sun, periodicity of, 379 
Sprengel on insects and plants, 415 
Stahl on phlogiston, 133 
Star, morning and evening, 11 ; -clusters 

and nebulae, Sir W. Herschel on, 281 
Stars, binary, 283 ; spectrum analysis of 

the, 344 ; movement of, 346 
Statics, Stevinus on, 80 
Steam, condensation of, 248 ; latent heat 

of, 242 
Steam-engine, history of the, 244; New- 

comen's, 245 ; Watt's, 249 
Steinhill on electric telegraph, 383 ; on 

earth acting as return wire, 385 
Steno on fossils in the earth's crust, 214 
Stereoscope, Sir J. Herschel on the, 335 
Stevinus on statics, 80 
Stewart, Balfour, cited, 338, 343 
Stokes, Professor, on dark lines in solar 

spectrum, 338 
Stomachs of animals, peculiarities of, 199 
Stone tools of lake-dwellings, 454 



TOURNEFORT 

Stoney on size of molecule, 364 
Strabo on earthquakes and volcanoes, 33 
Strata of England mapped by W. Smith, 221 
Striae caused by glaciers, 449 
Strings, laws of vibration in musical, 266 
Sublimation described by Geber, 44 
Sulphuric acid made by Geber, 45 
Summary of science of sixteenth century, 
80 ; of seventeenth century, 182 ; of 
eighteenth century, 289 
Sun, experiment to explain the movement 
of the earth round Ithe, 19 ; seen after 
setting by means of refraction, 48 ; ro- 
tation on its axis proved by Galileo, 90 ; 
his distance 108 times his diameter, 155 ; 
method of measuring the diameter, 155 ; 
distance from the earth, 158 ; holds the 
planets round it by gravitation, 148 ; 
meteors falling into, 310 ; atmosphere of 
vapours surrounding the, 341 
Sun-dial invented by Anaximander, 10 
Sun-spots seen by Galileo and Harriot, 90 ; 
Sir W. Herschel on cause of, 379; 
Schwabe on periodicity of, 379 ; their 
connection with magnetic currents, 380 
Switzerland, glaciers of, 448 ; lake-dwell- 
ings of, 454 
Syene, earth's circumference measured 

from, 29 
Syntaxis of Ptolemy, 32 
Synthesis, term explained, 399 
' System of the World,' by Galileo, 91 
' Systema Naturae ' published, 210 



TALBOT, Fox, on spectra of flames, 
338 
Telegraph. See electric telegraph 
Telephone, description of, 387 
Telescope, Roger Bacon's idea of, 52 ; in- 
vention of the, 87; Galileo's, 89; Kepler's, 
97 ; achromatic, 169 ; largest refracting 
and reflecting, 310 
Tessier, Abbe, meets Cuvier, 427 
Tests, Bergmann on chemical, 229 
Thales, science of, 8 
Thallium discovered, 338 
Theophrastus the first botanist, 17 
' Theory of the Earth ' published, 218 
Thermo-electricity, discovery of, 378 
Thermometer, invention of the, 118 
Thompson, Benjamin. See Rumford 
Thomson, Dr., on Dalton's theory, 404 
Thomson, Sir W., on dissipation of energy 
360 ; on size and vibration of molecules, 
364 ; cited, 338 
Thoracic duct, Pecquet on the use of, 112 
Tides, Newton on cause of, 152 
Torricelli on weight of atmosphere, 114 ; 

invents barometer, 116 
Torricellian vacuum, 118 
Tournefort's classification of plants, 142 



INDEX. 



509 



TOWER 

Tower, Hunter dissects the wild beasts of 
the, 198 

Transits of Mercury and Venus, 153 ; 
Halley's method of measuring, 155; De- 
lisle's method of measuring, 277 ; dia- 
grams of, 156 ; expeditions, 159 

Trianon, Jardin de, 207 

Tycho Brahe, his life and astronomical 
work, 75 ; Galileo and Kepler compared, 
99 . 

Tychomc system, 75 

Tylor, E. B., illustrations of refraction of 
light, 178 

Tyndall, Dr., on heat, 360 

T TNDULATORY theory of light, 175 ; 
^ explains interference, 318 
Upsala, Linnaeus's botanical garden at, 207 
Uranienburg, Tycho's observatory at, 76 
Uranus, discovery of, 281 ; had been ob- 
served by Flamsteed, 282 ; its irregular 
movements lead to discovery of Neptune, 
304 

VACUUM, Torricellian, 118 
Valleys, excavation of, 11 

Valves in veins discovered by Fabricius, 
109 ; use of, 109 

Van Helmont, chemistry of, 70 

Varieties, useful ones alone survive, 468 

Vasco de Gama sees southern stars, 57 

Vegetable anatomy, 137 

Veins, Galen on, 34 ; action of, discovered 
by Harvey, 109 ; valves in, discovered 
by Fabricius, 109 

Velocity of light measured, 172 

Venus, phases of, agree with Copernican 
theory, 89 

Venus, transits of, 153 ; used to measure 
sun's distance, 156 ; Halley's method of 
measuring, 155 ; diagrams illustrating, 
157; Delisle's method of measuring, 276 

Vertebrata, term explained, 433 

Vesalius, his work in anatomy, 65 ; ban- 
ishment and death of, 66 

Vessels and fibres of plants, 137 

Vesta discovered, 300 

Vibrations, light a series of, 176; of light 
complex, 326; calculation of musical, 263 

Vinci, Leonardo da, inventions of, 58 

Vital fluids, belief of alchemists in, 192 

Vitellio on refraction, 104 

Viviparous and oviparous animals, 140 

Volcanoes, Pythagoras on, 12 ; mass of 
lava thrown out from, 445 

Voltaic electricity, 259 ; pile, 261 

Volta on electricity, 257 ; his crown of 
cups, 260; his controversy with Galvani, 
259 

Volume and pressure, relations of, 120 

Von Baer on embryology, 437 

Voyages round the world, 56 



ZOOLOGY 

Vulcan, god of Volcanoes, 7 
Vulcanists and Neptunists, 217 

VK7ALES, moraines and erratic blocks 
v v of, 451 

Wallace, Mr. A. R., figures drawn by, 95 ; 
on natural selection, 463 ; on prolificness 
of birds, 466 

Wallis, Dr., his description of the Royal 
Society, 123 

Washington, telescope at, 310 

Water, composition of, 392, 403 ; rising in 
a vacuum, 114; latent heat of, 240; 
boiled by friction, 352 ; rise of tempera- 
ture in, by friction, calculated, 356; de- 
composed by sodium, 403 

Watson, Professor, on new planets, 312 

Watt, his early life, 242 ; not the first to 
make a steam-engine, 244 ; his separate 
condenser, 247 ; his double-acting engine, 
250 ; his partnership with Boulton, 250 

Wave-theory of light, 175 ; explains inter- 
ference, 318 

Waves of light in a crystal, 326 

Weber cited, 382 

Wedgwood, Dr. T., on sun-pictures, 331 

Weight of bodies explained by gravitation, 
151 ; of chemical elements, 401 

Weissmann on continuity of germ plasma, 
440 

Wenzel on law of definite proportions, 400 

Werner on rocks and fossils, 216 

Wheatstone on musical vibrations, 274 ; 
patents electric telegraph, 382 

William of Orange founds Leyden Univer- 
sity, 191 

Williamson, Prof., cited, 410 

Willughby and Ray, 139 ; on classification 
of animals, 138 

Winnecke's comet, spectrum of, 345 

Wohler on chemistry of organic compounds, 
408 ; cited, 410 

Wolff on metamorphosis of plants, 415 

Wollaston, Dr., observes dark lines in the 
spectrum, 333 

Woodward, his geological collection, 215 

World, first voyages round the, 56 

Worm, regrowth of divided parts of the, 201 

Wurtz, Professor, cited, 410 

"y E AR, length of, calculated, 45 
x Young, Dr., his life, 316 ; on inter- 
ference of light," 319; and Fre'snel on 
polarization of light, 324 ; his theory of 
colour, 328 

VODIAC, or circle of animals, 19 
*-* Zoology, Aristotle on, 16 ; Gesner on, 
67 ; Ray and Willughby on, 138 ; Lin- 
naeus on, 207 ; Cuvier, St. Hifaire, and 
Lamarck on, 426 et seq. ; Darwin on, 463, 
recent advances in, 474 



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